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.

ok, this is an area where I actually know something! I sold and spec'ed hardwood for a custom shop before my mommy-life. The information you are getting here is correct. Engineered floors will give you 1-2 refinishings ON A PERFECT SUBFLOOR. One of the issues that sometimes arises if there are inconsistanies in the height of your subfloor. Because there is thinner wood wearlayer (before you get to the engineered wood) there is the chance that you can damage the floor irreparably when you sand it. Now I only saw this saw this happen twice, once on a loft job and once in an older home. The loft was more subtle as it was over concrete, the old house more obvious as they were DIYers and picked engineered flooring to try to negate their irregular subfloor (they neglected to tell us that that was why they chose engineered, we would have talked them out of it had we seen the floor first) Neither of their claims to the manufacturer were fully settled because both times they did not follow the guidelines for floor prep. The loft job was also a materials only job for us with their GC laying the floors but he insisted he knew what he was doing. A good engineered floor will not be cheaper than most of your nail down options because the production costs are higher. Now having said that, GOOD engineered floors certainly have their place in places where you can't put traditional hardwood due to height restrictions or concrete subfloors. My boss had a great engineered floor in his basement and it survived a flood remarkably well (it was ash, Kahrs brand out of Scandinavia and one of the beefier engineered floors and one of the pioneers) My Grandmother also had a Kahrs floor in her ground suite condo and she LOVED it and I was impressed by the milling. I'm considering it for our basement because it's warmer and less echo-y than laminate There has been a lot of 2nd rate engineered flooring coming out of China and being labeled for all sorts of different companies. You should be able to tell an engineered sample because the layers are sandwiched together and the tongue will be a different wood than the top (showing) layer. Distressed finishes are usually more expensive because of the extra step in manufacturing to make it distressed. That is different than just getting a lower grade of hardwood like a rustic or tavern grade (in solid hardwood). Those grades have more character but they often don't carry a warranty and generally have a higher waste percentage. Another thing to think about---if you ever have to replace part of the floor, you will always be able to replicate 3/4" thick hardwood but engineered floors are more like tile, they change and get discontinued over the years. You could go pre-finished, save the hassle of site finishing but with the thicker wear-layer a 3/4" nail down floor offers. Only you will know if you can handle beveling or not. The changes in milling the last 10 years are huge. The bevel in your better milled wood is tiny. I like Canadian mills, Model or Mirage for pre-finished. Remember that if you ever re-finish, the bevel will disappear and you will, essentially have a site finished floor. One benefit that many people don't know about? With a prefinished tongue and grooved floor you can have a good installer cut out a single board (or more) from your floor if it gets damaged which is why we did a fair bit of pre-finished in new homes since inevitably we would get call-backs at move in to repair trade damage (@#$%^ plumbers and their big wrenches!). Prefinished hardwood deals the best with shinkage and expansion issues because the finish is on individual boards. Site finished floors are more labor intensive but the materials are cheaper (apples to apples). They are what many people consider the gold standard however there are more steps and you don't always know how it's going to look until it's done. There is more chance of finish contamination and trade damage during the rest of the building process. We refinished 100 year old floors. I loved the idea that there wasn't 4 generations of carpet and crap in the landfill. Definitely a forever floor and it can usually be re-sanded for all but the very worst water damage (think entire house under water for a few days) If you are going with a wide plank, keep in mind your species and humidity level (and your ability to keep humidity stable). The wider the plank (with 3/4" thick flooring), the more obvious shrinking and expanding will be. If you take a 2" wide board and it shrinks 2%, it isn't very noticeable. If you take a 6" wide board and it shrinks 2% the gaping will be more noticeable and in the case of a site finished floor *could* pull your finish apart. You'll need to find a flooring contractor in your area with lots of experience. Most of the best hardwood shops ONLY do hardwood. Beware of carpet shops and many of the big box stores in many instances. Make sure they are accredited with the NWFA (national wood flooring association) http://www.nwfa.org/member/ good luck!

There is a lot of controversy right now about the glues in engineered flooring making people sick. That being said...I just don't like it, you can always tell it's engineered and just looks cheap to me. With hardwood, you can sand it down if it gets damaged, with engineered, you can't.If it is anywhere near water pipes, you have to look into the future, a leak, or flood will ruin engineered..hardwood will dry out. Hardwood won't cup if it's been dried properly. Cupping is from wet wood (not dried down to 8% or less moisture)being laid down, then trying to dry, and having nowhere to go because it's been nailed down. It then cups.

Find out the wear layer for the engineered hardwood. That will help determine which is the better deal and product for the $$. Annied75 is right in that pine is a soft wood. It is not as hard as oak flooring. However, with that being said, all hardwood is susceptible to wear and tear and will show it over the years. The reason I ask for the wear layer is because it will help us determine how many sandings this engineered floors can withstand. The engineered floors we provide for our customers have a wear layer the same size as solid hardwood and therefore can withstand the same amount of sandings before reaching the tongue of the hardwood. If your engineered floor has a thin wear layer, the solid pine flooring just may be the better product for the money you are going to be spending since the pine floor will be able to withstand several sanding and refinishings. However, I read that you are going to be installing this over a slab floor in Florida. Since that is the case, engineered flooring is the way to go unless the pine flooring is going to be milled in an engineered version. Ask Hardwoods for Less if they can send you some samples before making the large purchase.