This thread answers most of your questions.
In summary:
1) Using the 3% H2O2 "gel" recipe I used, in the manner I used it, produces perfect deyellowing -- no uneven splotches whatsoever. Don't submerge compact Mac cases because you will harm the gray colored coating on the inside of the case.
2) Remove the Apple logo on the front of the SE/30 like I did, don't worry about the other labels. But keep in mind I did not put the gel over my labels (perhaps they got splashed a tad bit during the day, but I did not brush the gel on the stickers deliberately). Doing it the way I did results in NO DAMAGE to the stickers. The only sticker that was a tad bit discolored was the sticker on the bottom of my mouse, and that's because I soaked it in the liquid form of RetroBright all day, and it is a sticker that isn't coated well like the stickers on the back of the SE/30 housing. But honestly, the slightly discolored sticker is on the BOTTOM of my mouse so I won't see it, and it wasn't discolored in a bad looking way anyway, so I don't think about it with any regrets at all.
3) Disassembly of an SE/30 isn't that hard, it just takes about 30 minutes. Just remove all the screws you can see. And the ones holding the CRT are pretty easy to spot. And you really don't need to worry about the CRT as much as some web sites make it out to be. Just turn off the SE/30 and unplug it when you are doing the disassembly.
4) Yes, the keyboard keys come off, no matter what keyboard you have. I used a flat head screwdriver to carefully pry up the keys on my IIgs keyboard. I then immersed the keys in the liquid for of Retrobright (since you don't need much liquid for that, and there is no metal to damage, unlike the inside of the compact Macs housing).
Good luck.