Ok so they all might seem pretty ignorant questions (well.. they are..) but im just starting and haven't had many housings in my hands (plus i hear that camera stores don't like to lend out housings so that you can just have fun taking them apart... 
).
About the buttons: they work like a stuffing box, an o-ring seals against the button stem and the spring is there just to contrast the water pressure that would push the button, the "washer" on top of the o-ring, where the spring sits, is there just as a base for the spring and to keep the o-ring in place but doesn't contribute in helping the o-ring seal. Changing to stronger springs permits to use the housing at a greater pressure (provided that everything else can stand it)
Did i get all this right or im missing something here? (any link to pics that can show an "exploded" of the wheels?)
Where are the most common places the water comes in? the buttons, the port or the seal at the back?
Ive read of housings having a double o-ring at the back and/or on the buttons but why i don't see any having a sort of sealed "boot" inside the housing that would stop water if comes in from the buttons?
Beside electronics (usb, remotes in the housing) is there any other way to work the controls? im having this mental picture of a completely sealed button using a liquid, like oil, in place of the metal stem, obviously no o-ring and just the spring inside... if the "envelope" is permanently sealed against the housing there aren't possibilities of leaks, but that's just a bizarre idea for now (well, i used something similar on remote controlled airplane models before, so...).
What are, if any, the buttons that are superfluous because relate to functions usually completely unused underwater? im trying to understand how much people actually stay there tinkering with camera functions while diving and how much is actually pre-set before the dive.
About ports: flat is for macro and domes are for wide angle. Would a dome which isn't completely hemispherical (a not too deep dish) be a compromise that gives somewhat ok results in both or just bad results for both?
As a beginner, if i can choose only one, which way is best to go? (not getting anything yet, just as information from your experience)
About lenses: how do wet lenses work?
Are they a normal lens inside its own little housing? wouldn't then the first element be exactly comparable to a dome or flat port, with the refraction story happening inside the lens?
Is it just the lens mount that fixes the whole thing to the camera or the housing, with enough strength to make a seal?
About IR: if i have a camera with the IR filter removed underwater it should behave exactly like it still had the filter since its the water that does the job (that's the first one absorbed right)? what sense has then IR photography underwater?
About lights: better a flash or a fixed light like LED for example?
I know that the lights should be on a flexible arm to be positioned depending on the subject but if you have a fixed flash (not on-board) in a compact setup where would you position it? top corner pointing completely inwards or top corner pointing forward to illuminate big subjects and with just the edge of the light cone hitting a close subject in front of the camera?
I know its long and that some questions can be pretty silly but....
