You need to do a little more archeological digging still. You need to know the whole construction of the floor before you can decide how best to install something new. I'd take up that plywood piece in the kitchen and see what's under it. It's higher than the surrounding floor, so needs to go. You should also be able to see from there what subfloor is under the original kitchen hardwood. It's too bad the space under your entryway is finished, but I'd still do some exploring from below to see what's under there, and to figure out the fix to stop it from squeaking. Is it drywall below or a drop ceiling? I know it probably seems like a pain to tear out drywall, but if you cut out a clean patch, like 2' x the width of the joists, it'll be relatively simple to repair. Just make sure to cut it down the center of the joists so that there's room to screw the patch piece to it later. Cut the hole under the area that squeaks the most, if you can. Have someone walk on and watch the floor from below to see what's moving. It might be as simple as pounding in a couple shims from below, or face-nailing a loose board from above. You want to find out what's underneath the hardwood. It might be laid directly on the floor joists, or there might be 10" wide boards that the hardwood is nailed to. Another thought is to take out a board in the hallway, since that's not original and you want to replace it. See what the subfloor is there. I am a bit puzzled at why, when you've stripped the kitchen down to the original hardwood, it's still higher than the hallway floor. Is your current surface perhaps not the original kitchen hardwood? Peeling back the plywood area will help determine that. BTW, I haven't heard of that stop squeaking product you linked to, so can't offer any personal opinion. And don't pour self-leveling compound over top of hardwood. It needs to go over plywood.

Not an expert but I do not think anything but time may help. Perhaps a fan or dehumidifier to dry the floor quicker if it is a very recent leak?

Greetings, The picture (faux or real wood?) could be Red or White Oak or Ash, Ash is similar grain characteristics as Oak. It's likely Red Oak (least expensive) as White Oak typically has a rib-boning effect. I'd take your sample to a professional paint / stain store such a Sherwin & Williams and ask them. They can do custom matching using a computer. Good Luck. William

A light or no stain on red oak will give you pink floors, so best to go with a medium brown. A medium tone is also classic - as styles swing back and forth from light to dark I think it's best to be in the middle. Who wants to refinish their floors every 5-10 years? This way you won't have to do it again until they need it instead of when fashions change. Just don't go too cool on the brown - they shouldn't look gray. Gray floors are definitely out on the coasts - if this hasn't happened yet where you live it is on its way.