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.

Traditionally a nail-down "wide plank" hardwood receives "glue assist". That is to say glue is applied to the back of the planks and then nailed into place. Your problems will be SHRINKAGE due to VERY DRY conditions. A wide plank is VERY tricky to install in DRY climates such as yours. And to be clear, "wide" is anything 5" or wider. Your 7" wide planks are VERY wide. The wider the plank, the MORE it will shrink. The more it shrinks the bigger the gaps (where water and urine can fall into). The more it shrinks the unhappier you will be. A solid, narrow strip hardwood (such as 3" wide planks) would be the best option if you want wood. Some of the worst shrinkage/splitting/checking occurs in DRY climates. Humidity is SUCKED OUT of the wood so quickly it starts looking like 20 year old cedar shakes. Please check to see if you can ADD humidity to your entire home at the touch of a button (whole home humidifier). If you do not have this device, I highly recommend you purchase one. I would suspect $6K should get you what you need - but that number is highly dependent on size of your home and the type/size of your furnace/duct work.

Leather is the most 'recognizable' pattern for cork (other than the ground up cork board look). When it is laid it looks like hardwood flooring using 'shorts'. It has a bit of a brick look to it. Ignore the 'pink' in the samples. The pink is the very first colour to fade away. It takes a few months for the pink to disappear but once it is gone the cork (Leather and Logan) will look more like oak in tone (yellowish with some hints of green and some gray). It is a 'directional pattern' which means it has a 'linear' sense to it. The Logan is the most expensive cork pattern you can get. The slices of pattern are random. They are hand cut and hand laid. It takes *roughly an hour for 1 person to arrange 10sf of the pattern. It is STUNNING. It looks more like stone. It is random...did I mention the pattern is random? Leather and Logan can have the extra 2 coats of the Loba 2K Supra AT = super tough. The Latte is a FANTASTICLY tough finish. It has the polypropylene finish on it. This is the 'non-vinyl' product Cancork sells. It is tough....right after that it is SUPER TOUGH. And then for good measure, it is TOUGH!!! For a Rental property, the Latte is a product I would recommend. It does NOT need the Loba product. That means you save $1.50/sf RIGHT AWAY. It can handle 3mm or 6mm cork underlay. If you are looking for temperature control, then I like the 6mm underneath...but CHECK your door heights, etc. All you need to do is take your floor sample and the underlay sample they sent you (their supposed to do that...sigh) and see if it 'slips' underneath the doors in your home. It is that simple. I hope that helps... As for the Tacoma...I'm guessing you are looking at KILOGRAMS (700 kg) as your weight limit = 1540 lbs. The weight of a standard skid of cork flooring = 1000sf (ish...depends on the product) = *roughly 2000 lbs. And the skid sizes are PERFECT to fit between the wheel wells of a truck bed. I've watched this stuff get loaded into pick-up trucks for 6+ years. A forklift operator can drop that baby into your truck (so long as you do NOT have a 'cap-it') and off you go. If you only have a short way to go, the 2000 lbs won't be much of a problem...I just wouldn't do a trip to Bella Coola with it. ;-)

So long as the subfloor is reasonably flat the cork will do all the flexing you need. As a cork expert, I've used 6mm cork underlay to "eat" 1-2mm worth of variation. Because cork is solid but not rigid, it will do a little bit of correction for you. Besides, if you glue down the floor you have to glue down the cork and that takes +++glue. We call it a double stick. It can add up to $2/sf just for the glue. And you can't lay the hardwood if the cork is still damp from the glue. If you float the flooring you float the cork. Simply lay the cork sheets PERPENDICULAR to the direction the floor will run. Like most things in the building world, it always makes sense to 'off-set' your layers. If you would do it with plywood sheeting you might as well continue with the cork. It takes 30 seconds to determine the direction of the hardwood. You simply run the cork in the other direction. The issue won't be the cork or the glue. It will be the width of the planks. Those wide planks will move more than you ever thought possible. Regardless of the structure of he plank, the wide planks will be MUCH more unstable than a narrow plank. That's why the home's HVAC system should be investigated and upgraded - if needed. You MUST keep the indoor humidity stable between 45%-55%. If your current system does NOT have that capability I suggest you take that $2/sf savings on the glue and use it to invest in a whole home upgrade.