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.

You know, to me "fake" is not that big of a deal in some things where cleaning or lifespan can be an issue. Yes, like you, I would love authentic everything including hardwood floors. But I have cats. I always have and I always will. They bring absolute joy to my life. I have lost all three in the last couple of years, Amara my most recent loss left us last week, but more will come. I also want beautiful things around me. My description of my home is "comfortable elegance." Neither word has any more emphasis than the other; both are essential to creating a home I love and love to share. But cleaning and damage is a big deal too. I have no intention of spending a lot of time that would require high maintenance. I look at my faux Christmas tree as gorgeous even without the scent. (I buy real wreaths to hang high enough so the cats cannot get to them just so I can get the scent.) I look at my LVP flooring as incredibly beautiful because I got a color I like and any accidents including hairballs are easy to wipe up and I never have to worry about it. (Ditto if the washer ever fails.) If you compare one to the other you may find yourself adding regret and judgmental attitudes to your perspective. But if you acknowledge their differences and choose one, based upon the advantages you prefer, then I think you might find you will have few if any regrets. You won't mourn what you can't have (both easy care and real hardwood) but instead you will embrace and celebrate what you did choose because it makes you happy. And that is all that matters.

I am thinking about using a shellac finish and sealer on this hardwood, which will be the floor for a kid's room. This Bullseye traditional finish and sealer product from Zinsser seems widely used and well liked: https://www.lowes.com/pd/Zinsser-Bulls-Eye-Clear-Shellac-Actual-Net-Contents-32-fl-oz/3449840 This particular product says it is clear, and I think there is an amber tinted version. Can shellac be applied without problems to hardwood? I believe I could put poly on top of the shellac and be done. Is this right? Any tips or warnings? There is also this Sealcoat by Zinsser, which does not appear to be shellac based. https://www.amazon.com/Rust-Oleum-Zinsser-854-Sealcoat-Universal/dp/B000C02BXW/ref=sr_1_3_mod_primary_new?dchild=1&keywords=zinsser+shellac+sealer&qid=1610393849&sbo=RZvfv%2F%2FHxDF%2BO5021pAnSA%3D%3D&sr=8-3 Would the Sealcoat be a better option to just put over the hardwood? I have read elsewhere that shellac can be applied over poly, which is good since I don't know what is on the existing floor. Other places say shellac could be sanded after application, so when we have a chance to completely sand and refinish this floor, I would probably want to do this. Does this sound like an acceptable temporary fix, or is there something I should consider before proceeding? Would shellac ruin or damage the hardwood. I am also thinking about LVP, but I am concerned this hardwood floor is not flat enough for that. I understand the subfloor for LVP must be 3/16" within about a 1 foot diameter to work. Any ideas about this? Is there a way eyeball this floor to determine whether click LVP could be put down? Thanks!

First of all, I've taken carpet out of many areas where there were original hardwood floors underneath them. A hardwood floor is not structurally worse than plywood; in fact it is better quality wood and therefore structurally better. So, if I were going to do LVP throughout the home, and I was worried about the subfloor (the plywood part), I would pull the carpet up first to see what is under it. If there is structurally sound plywood under the carpet then you can make your decision from there about the hardwood. You could always raise the carpeted area to the level of the hardwood and do the LVP then, which could potentially save you money, depending on the size of each room.. Or, you can look for a reducer (strip that connects two different kinds of flooring), but that probably won't be your first preference because it will create a lip and looks old fashioned. Second, in my area (midwest) the market for good used carpeting and any hardwood flooring is so hot that pre-pandemic I advertised an entire second floor of carpeting, in good used condition (no stains, but used) on craigslist and within 24 hours it was gone. People came and took it all, padding and everything. Same with hardwood - family members took theirs out, replaced it with LVP, and sold the used hardwood at an overall profit. It is not hard to take carpet out; hardwood can be trickier depending on how it was put down. Seriously, I'm a 50 year old woman and with a claw hammer and some gloves I could get that carpet up in an 6 hour day, pad and all. Two preteens could take it up in half that time. Now if the subfloor is concrete (no basement), then you may have to scrape the glue off when you remove the padding, but even then glue is usually just in targeted lines, not evenly spread all over, so there is not much to get up.