Asking the real questions:

Do exos take showers?
Do they have someone they go to so they can get a new paint job? Or fix dents?
If exos can eat and drink how does it come out??
Exos don’t need sleep, but they like to sleep because it feels human… so can exos dream?
Can exos be modified- gun arm or longer legs?
Do they worry about rusting? Or creaking- like they need to oil themselves every now and then?
Are their movements loud because their bodies are made of metal and metal clanking against each other is loud?
Are exos heavier than an average human?
Can exos taste the things they eat/ drink?
Can exos get drunk?
If exos were designed to be soldiers… are all exos skilled fighters?
What’s the Long Slow Whisper?

I am once again advocating for a badass Exo spa / modding garage / tattoo (etching?) studio Combination Establishment type... thing... in the Tower or somewhere around the City, helmed by my absolutely-not-a-self-insert yet-to-be-properly-designed OC, who'd be armed with a paracausally-charged tattoo machine (so they're able to make marks that stick). I also wanna know how Ada got those Jingdezhen porcelain looking stunners on her.

As for the eating / drinking thing, I'm fairly sure Exos can eat and taste and get hammered just based off uhh,, Cayde being a ramen fiend & frequenting the bar that got blasted in that one cinematic. I don't have specific lore bits to point you towards off the top of my head but Resident Tunglr Lore Historian @thefirstknife prolly does.

Exos do dream. They have a recurrent shared nightmare about uhhh murdering loads of people including their loved ones on their way to a Mystical Tower of some sort... and this is linked to the 'Long Slow Whisper' in that both seem to be the influence of the Darkness and/or Witness (?) which their machine consciousness is partly powered by thanks to the Radiolaria Clovis used to create them... IIRC

thefirstknife

Hewwo.

Yeah, Exos can taste and enjoy food. It's important for their mind to feel human, since they don't really need food for sustenance, just to satisfy the human mind. So being able to taste is kinda essential.

It's unclear whether they can get drunk. Cayde certainly claimed so, but it's Cayde. He's not the most reliable narrator. I'd say they can get drunk because, again, the point of drinking is to simulate humanisms so if they drink a lot and nothing happens, it would risk triggering DER probably. However, maybe it can be "turned off" or modded.

Speaking of modifications, yeah, they're definitely possible. Again, Cayde jokes at the end of the Red War (when his arm and leg are blown off) that he'll replace his arm with a rocket launcher. I'm pretty sure that was just a joke, but it wouldn't be surprising that Exos modify parts of themselves. The only problem is whether they know enough about the technology to do it (and if they have the necessary equipment). I think after the re-discovery of Europan facilities and DSC, the Exo modification market boomed.

Also speaking of simulating humanisms, we have a direct mention of an Exo crying "simulated tears." So they clearly have a way of producing or repurposing liquids they consume. Which leads me to the very heavily debated topic of: do Exos need to go to the bathroom.

Seeing as they DO eat, that food has to go somewhere. I'm assuming some (or all) of it gets turned into energy for the Exo so it doesn't go to waste. However, Clovis specifically mentioned "digestion" as one of the humanisms Exos need in order to not start tearing themselves apart. This can feel off because a lot of us would probably prefer to never have to go pee or poop ever again, but the lack of a digestive system and the need to pee is something that would, over time, become very strange (especially paired with the lack of other humanisms Exos initially didn't have). The mind simply starts thinking the body is dead.

I called in a team of psychologists to interview the next cohort of exos and make recommendations. They have settled into the Eventide habitat and have proven immediately very helpful. It was obvious to them that the root of the problem lay in the deficient exobodies I had supplied. Deficient how, I demanded to know. They did not suffer human weakness. They never needed to eat, drink, breathe, sleep, micturate, or dream.

Apparently, this was the problem.

I had assumed that the need for these irritations would pass since there would be no shortage or accumulation of poisons to trigger them. But evolution’s tangled ways cannot be so easily rationalized. I was wrong. Their brains concluded that all of their internal processes failed. No digestion, no breath, no heartbeat, no sense of interoceptive health… all signs of death.

From this we can safely say that everything that humans need and want to do applies to Exos perfectly (aside from the individual Exo being somehow deficient, broken or modded). Everything humans do has to be simulated for Exos. Breathing, heartbeat, hunger, tears, even digestion and pissing (or as Clovis would say it, "micturating"). This includes any and all sexual stuff (aside from pregnancy).

It's also safe to say that Exos do everything in the same way humans do. There is no need to imagine them being weird or alien in some way just because they're not organic. Exos are real human persons:

"You are not a robot. You're not even a total-replacement prosthetic. You are a body, and a body is the same thing as a person, and a person deserves respect. Basic transhuman hermeneutics."

On the topic of modifications, we have a lore book about Clovis' experiments (warning for some really gruesome descriptions). So clearly there were attempts. It's unclear if any of them worked or if some of them could've worked if not done by Clovis.

Golden Age humans were fine with genetic modifications and splicing genes with animals, so if a Golden Age human was living just fine with chimp-spliced genes, then an Exo would probably also be fine with some heavy and/or specialised modifications.

It doesn't seem that all Exos were designed for the same purpose. Most of them were capable of doing military stuff, but not all had the same model and not all did the same jobs. This mentions an Exo that "had the build of someone's mom" (lmao). This whole transcript is nice because it features many Europan Exos with different experiences. Hector-6 for example remained a psychologist even after becoming an Exo. Mia-9 notes that she feels her body is wrong and not the same shape she had before (as well as saying that Elsie got a custom body that's "the same shape as the one she had before.")

The primary idea is for them to be capable soldiers, but there's always a need for extra personnel even in the military, as well as the need to make the idea of Exos commercial. So different models are necessary. Clovis planned on turning his whole family into Exos so they could live forever as his legacy. He certainly didn't plan to send them all to die in some war.

And yeah, Long Slow Whisper is something that all Exos can sense/hear due to the fact that they've been created by "purifying" radiolaria with Darkness. They all have strange dreams and sometimes hear something speaking to them. The dreams are not always about the tower, but in most cases they are. Here's lore on a peculiar dream Saint-14 has.

We can assume that the tower they all dream about is the strange tower that Clovis and his team found on the Vex planet Volantis (the only structure that didn't fit the same architecture as the rest on the planet). The Whisper is likely residual from contact with Darkness. Description of Volantis (Entry 7) and how there's a strange tower that doesn't appear like it belongs there:

We ventured out of the ruins, onto an island of living glass, broken by fissures of deep green light and reservoirs of white fluid. Around the glass, a shallow sea trembled with tiny, intersecting waves. In one direction, a cloud of mist obscured a shattered tower, its form uncannily different from the surrounding architecture. Above us loomed structures linked by bolts of lightning, reminiscent of the Citadel ruins on Venus.

This is already the length of a novel and I haven't even touched on Ada-1, who is a unique Exo, not made by Clovis and not using Vex radiolaria and Darkness. It's unclear what was used to make her, but it's implied it was some form of Radiance technology that Black Armory was using (which is probably Light-based). Ada does not appear to suffer from DER, does not appear to need to eat (she doesn't have a moving mouth so if anything, she doesn't eat the same way other Exos do) and she has never had a reset (she's been around since the Collapse, making her one of the oldest characters and among the oldest non-Guardian Exos).

Another unique Exo is Felwinter, who was not made from a human mind but as a part of Rasputin and worked as Rasputin's mobile frame. However, the Traveler clearly considered Felwinter to be an independent living being and he was rezed as a Guardian.

I recommend reading all Beyond Light lore because it's a treasure trove for Exo stuff and really went deep into a lot of details. There's still things we don't know and perhaps we'll get some new information when Ana finally boots up Rasputin into an Exo (that will be the first Exo made since the Collapse).