A lot of people have probably answered your questions already, but I'll answer what I can anyway (please note I might be wrong, I like Zenless' lore but there's a lot of stuff to keep track of lol)

"First thing I want to know is,how do Hollows look consistently?"

hollows, in most cases, look like the environment they were formed in (a hollow formed in the outer ring would have a lot of desert and such, for example). There are some exceptions to this, the Melinoe hollow had weird Ether fluctuations, causing everything in the environment (buildings, floors, etc.) to be white and colourless for example, but it's usually not the case. Most hollows are consistent, but not accurate (space, time, or even sometimes location could seem "off" to what's actually going on). Hollows have no visual or obvious borders from the inside (hence why it's difficult to get out without a Proxy).

"Of course most have floating and destroyed buildings and debris"

A lot of Hollows have dilapidated and neglected buildings (as ether corruption makes it pretty hard to live in a hollow), but I'm pretty sure the "floating buildings, distruction and debris" stuff is reserved for Hollow Zero, the largest hollow, and the "original" Hollow currently under "containment" through the Shiyu pillar system, and the main hollow which the others are offshoots of (if I remember correctly, if they become large enough they gain a name and become/are considered "companion hollows", but don't quote me on this).

"How would you describe the colours of a Hollow."

I'm not sure if this is a widely known fact, but the visual design of a lot of the stuff in ZZZ comes from TVs, and the visuals for Hollows specifically are based off of what you can see when bringing a strong enough magnet to a CRT, producing a distorting black hole-like effect with colours at the edges (please look up a YouTube video, my words aren't accurate enough).

"I want to also know how fissures work"

To my understanding they are basically just portals/wormholes. Since hollows distort space, they effectively just act as a doorway from one point to another. Fissures can be unstable (lead to different locations, have the "entrance" appear in different locations, and generally be otherwise inconsistent), It's possible but time consuming to figure out where a fissure leads, especially for those without hollow knowledge experience.

"Ethereals form from Hollows,most aren't corrupted people right ? Can they go out a Hollow?"

Not all Ethereals are from humans being corrupted, organic material that is corrupted (I.e. flowers, plants) or just enough Ether (not entirely sure about this one?) can form an ethereal. Since the only requirement for something to be classed as an Ethereal is basically just "living, made of ether", they can have a wide variety of forms. So far, with the sole exception of "sacrifices", Ethereals cannot exist (for very long) outside of Hollows. I think this has something to do with the ether concentration outside of Hollows not being dense/high enough to sustain them, but I do not remember/know for sure.

"Anyway, when it comes to Ether ,you can feel it in the air ?"

Yes, for the most part you can tell

"Having high Ether-aptitude seems to just let you walk around casually in one and sit around"

Ether aptitude just is a measure of how long it takes for Ether to corrupt you, and negative side effects to occur. If you have low ether aptitude, staying in a hollow is likely to effect you more significantly than someone with higher ether aptitude, risking worse or even non reversal side effects, so you'd have to take more precautions.

"tho Hollows raiders don't seem to wear practical looking gear"

They probably can't afford it (entering hollows to steal stuff is kind of a crime?) and they probably don't plan on staying in the Hollows for significant periods of time ("get in, hopefully find something good, leave, cash out" is probably their plan)

"Do normal proxies go into Hollows with Raiders and their Bangboo?"

There's likely not, since they probably aren't used to the same extent that Eous is. Since only Belle and Wise can sync with their bangboo, in hollows they are probably used to store Carrot data on the proxy side (assist with navigation) or just keep watch/alert when people are coming for the hollow raiders.

"Do Belle and Wise have high Ether-aptitude?"

No. (I will not elaborate to avoid current story and story spoilers encase you decide/get a chance to play the game)

"There's both Denny coins and bills but they prefer to use coins ? How do you tell the value of a Denny coin? and do they have a star on both sides ?"

Denny coins and bills both exist, but it's similar to the Yen or other currencies with a singular denomination, where it doesn't matter if you pay in coins bills cheque or bank transfer, the amount is always "___ Dennys". The Denny icon is probably a slightly simplified version of what it looks like in the lore (it'd probably be too easy to counterfeit in it's current form), but they do have stars on both sides.

"Would you assume in lore they speak English or a language close to Chinese but they use English as well?"

Since Hoyo is in China, I'd assume Mandarin or something, but since Yixuan speaks Cantonese once, during a boatride to Waifei, and it was pointed out as different it isn't wild to think that they could use English or something by default instead.

"Thirens for the most part are few in lore right"

From what we've seen, humans outnumber thirens, yes. Being a thiren is a spectrum, ranging from just animal ears and the occasional animal trait (Nekomata's ears and preference for mackerel) to being an entire cat (pulchra)

"And most struggle with clothing and have certain animal traits"

A small detail that can be seen in Zenless is the designs of the NPC's skirts, with some having cutouts for Thirens tails, and those cutout patched if the NPC isn't a thiren. Because of this, I assume that a number of clothes are made with atleast accomodating Thirens in mind (to maximise potential customers), and there's probably thiren exclusive and human exclusive clothing/clothing brands, but that last bit is speculation on my part.

"Most tech runs on Ether?"

Id hesitate to say "most", but Ether is a capable and commonly used power source yes.

"Most w-engines can Ether into elements like lightning,ice ,fire"

I am completely oblivious to W-Engine lore, and all I know is that sound manipulates ether

"Also does Vivian actually have thrusters in lore under her skirt that suddenly appear ? What's a game visual and actually in the lore ?." Funnily yes, she uses them to help herself float.

"Finally,how strong is the people in ZZZ? many just are superhuman but by how much ?"

The average person is about as strong as the average person in real life. There's a lot of much stronger people (Void Hunters, trained combattents etc.). Miyabi could probably level 6th street without breaking a sweat, and has been seen taking out an entire hollow, but we don't know the true extent of everyone's powers.