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.

Those "gaps" are mild. They are normal. They are expected. They tell the story that they are original. They are meant to be there. The new floors will eventually do that too...which means they will match (eventually). It might take a decade...but it will happen. And don't forget that once everything is sanded down, you will be VERY surprised at how those "gaps" seem to go away (visually). Why, you ask? Because some of that is dirt. Once the floor has been sanded down (1-2mm of wood is taken off with the sanding), the dark material between the planks gets shaved off as well. And voila...they look cleaner (because they are). Relax about the absolutely normal spacing between planks. Unless you have museum quality climate control, this LITTLE bit of shrinkage is normal and to be expected with every floor (especially if it is 30 years old).

As Oak & Broad suggests the match would be SUPER easy. Red Oak is very common and very affordable. If we assume the hardwoods are original (finished in 1997), they are 22 years old (and counting). That means it is time to get down to business and figure out when to do a full sand/refinish. If you wish to add hardwoods to the bedrooms then NOW is the time to do EVERYTHING. A hardwood flooring store (Ma and Pa run/operated for 20+ years) will have seen this/done that for the majority of their career. This is their bread and butter. You will get an EXCELLENT price (wood + install + sand/refinish existing/new wood) when you put it in combination. You get this type of a discount because the professionals are ALREADY scheduled for your home...they are ALREADY THERE. Another day or two to get the whole job done is a drop in the bucket for them. This is super easy for them to schedule. If you were thinking of dropping in some site-finished stuff from HD (or the like) you would STILL be faced with a sand/refinish of the ORIGINAL stuff in the VERY NEAR future (the next 1-3 years...at most). That means paying for two crews to come out to the house and disturb your home twice. And you will pay for these visits twice. I know it sounds tempting to throw down some site finished hardwood ($4/sf + $2.50-$3/sf for install) right now, but it will end up being MORE expensive at the end of the day. Please check out your locally run hardwood flooring store and ask them to come out for a quote. They would be happy to do so. Let them know that you would like an estimate on installing "the same" in the bedrooms with a full sand/refinish for EVERYTHING. They should be able to come up with a quote for your situation very quickly.

I'm not sure what LVT is. :) I have an appointment with the flooring person for Saturday to test out samples. Cherie, we hate forced hot air because it bothers my and the kids' asthma and allergies so I am actually very happy about these baseboard radiators as radiant heat is much easier on the lungs since it's not blowing hot air all over the place. There is central air for the summer months. We live in Northern NH... it gets cold here for sure. I am going to keep the tile in the kitchen for now and the rest will be new flooring *all going in the same direction* ! We are ripping out the red carpeting, which is in all four bedrooms as well as on the stairs. We want to replace that with flooring and we don't want yet another type of flooring in the house so it makes sense to do the living and dining room as well. When we reconfigure the kitchen, we'll have to match it up and remove the tile at that time.