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.

kge9, Thank you so much for letting me know! I think 4" trim would look nice if it is above the floor. Right now I have almost 3.5" trim that is partially covered with the thick rug and padding so 4" not covered will look nice and wide for me. I would love it if it came primed. Maybe I can suggest if I buy it and the installer installs it to save money. I feel I can also paint the trim but not the walls. I don't have baseboard heating (wish I did) since I forced hot air heating with vents on the floor. I would love it if the quarter rounds could be skipped! How much space did you leave from the floor to the wall? I can't believe all the furniture is out of those three rooms and I can't believe how much furniture I had in those rooms. I definitely plan on just using my dehumidifier to keep some back files in my garage since I don't want to move 3 of the 5-drawer 42" wide file cabinets back into my home office rooms. I want more of my walls to show and more space to walk. kge9, any pictures of your new trim with the tinted white you planned on using.

Hopefully not corrugated cardboard because it compresses over time. "Should they have been putting down a sub floor to raise the whole thing up?" That's often my suggestion. How bad? Pictures would help.

I don't know what to say. The idea that anyone would consider junking oak trim and replacing it with MDF (a fancy name for thick cardboard) is completely alien to me. So is "the wood grain will show through and look bad." It wasn't all that long ago that manufacturers of builder-grade doors and trim were embossing faux wood grain texture into the surface of their "products" so they'd look like painted real wood instead of Masonite -- flat compressed glue and sawdust. But then, I'm kind of old. :) It's interesting to see this change in taste. I may be missing something, but it seems to me that people now seem fine with -- even aim for -- a smooth, even, plastic-like solid-color finish for trim, cabinets, even walls and ceilings. Wood is out, paint is in. Homeowners who can't replace their finished natural wood paneling, cabinets, and trim ask how to paint them. Years ago, probably in the late 1960s or early 1970s, I read an article that mentioned how new, cheaper building materials have always tried to imitate the old, expensive ones. (Besides interior trim, another example of this is wood-textured vinyl siding.) The author said that eventually decorators appreciate and use the new materials for their actual native characteristics. I guess it's happening.