It is your home. You did the research, made the decision and are happy with the results. We have remodeled and installed white oak T&G in our kitchen dining, hallways and are very pleased with it. The living room had old old vertical grain fir and I repaired parts of it, refinished it and we like it a great deal. I guess my choices make me a traditionalist, in flooring at least. What I do not like about manuf flooring is the beveled edges. It catches and accumulates dirt in the seams. I guess I like the dirt spread out evenly on our smooth floors. We were fortunate to have a good floor guy. That is important. Everyone is afforded their own biases and preference. Both my daughters love their engineered floors. Another instance where I went wrong. Darn!

It probably makes no difference structurally. It might be easier to use plywood in that it comes in different thicknesses so it would be easier to achieve the correct height of each riser.

I had tile in my last home and moved to a home with carpet everywhere but the kitchen (yes, even the bathrooms had carpet (yuk)). After 20 years my joints could not withstand the impact of living on tile floors. Choices were to replace the carpet with Carpet - It is soft and quiet. It gets dirty and is hard to get clean. Muddy paws from an active puppy while delandscaping the yard was a nightmare. Hardwood - much more expensive - harder than tile or LVT to maintain, would require purchase of area carpets to protect. LVT - cost efficient - low maintenance, limited lifespan (20 years ish) I'm 59 - 20 years I won't be able to see what it looks like. Can add area carpets for aesthetics, but can eliminate the trip hazards of area carpets as I age in place. Engineered hardwood seemed to have the same cons as hardwood, but cannot be refinished over and over again - thin layer of wood. I decided to replace the carpet with LVT, I am doing one room at a time as I renovate, but am very happy with my choice. I bought Downs H20 from Cloister's Flooring America. It is waterproof and is manufactured by Coretech for the CCA Family of flooring companies. Same product, different name at each company website. Different price at each store (store not company level, two different Flooring America franchises had 2 different prices). Difference from highest price to lowest price was a difference of $2.00 per sq ft - I was covering 2000 sf, so this was a substantial savings. I loved the franchise I picked - Cloister's Flooring America. Other franchises really pushed the professional install - Cloister's seems to cater to the DYI folks (Owned by a Mennonite family). For $75.00 they send one of their installers out for 2 hours to teach you how to lay the flooring and they will rent you a tool kits that has everything you need to lay your floors. I bought one box of each of two colors and could exchange the one I didn't pick when placing my full order. I also got an additional $500 off because I hadn't placed my order yet and they called because they were having an anniversary sale. I hadn't called because I had a heart attack and was in the hospital when I got the call. They gave me the $500 off and told me I could call when I was home and feeling up to ordering even though the sale was just for the week. They even helped me with the layout plan. Told me to use graph paper and tracing paper. I drew out my floor plan on graph paper and traced the outline of the flooring pattern on the tracing paper. You place the tracing paper over the floor plan and move it around until you have a placement that doesn't leave you with little 2" strips anywhere. You do have to be exacting in your measurement and drawing of the floor plan and lay out enough pieces to get exact measurements for your tracing. I didn't find this method on the internet anywhere - most have you plan from the center of the room, but this worked out really well for me.

About the 'cork', I can answer that. I'm actually a cork flooring expert. So...here we go. You cannot glue down cork underlay to 'finished' hardwood. Again, the glue has issues with the finish. So once again you are looking at a sand/refinish. Now the floors are sanded you can glue either the new hardwood down or you can glue cork down. The cork gives it NO stability (not like plywood). You would still have to run the new wood perpendicular (the other way) to the current floor. The glue you need will have to be a water based product. You will need DOUBLE the amount of product. You need to glue the cork (it will get SOAKING WET...that's OK...it will dry/harden in a FEW DAYS). You wait until the cork is dry and then you glue the hardwood, in the opposite direction, to the cork. It won't give you the 'plywood option' of keeping the same direction of the old hardwood. The glue will 'almost' ruin the old wood. I've seen people try to 'scrape up' glued cork underlay. It takes days and days and then you have crumbled cork everywhere. And the sanding down of the old wood = huge effort because of the glued crumbs and the sheet of glue on the wood. Horrible. Just horrible. I can see this is upsetting you and I'm sorry. What I HIGHLY recommend is you GET OUT of the 'floor part' of the contract. See if you can do the flooring using someone other than this guy. This person is using the ol' Contractor as flooring dude routine. If you believe you are 'being had' you can see if there is a way to nullify the remaining contract (the stuff you haven't paid for). Then you can find a real pro to do the flooring. The way out of this = having a clause added that states, "All flooring to be installed to NWFA Handbook, Best Practices and to MANUFACTURER'S requirements per the installation instructions." As soon as a 'flooring hack' takes one look at your requirements and they will run for the hills (at least for the flooring part). You can always find comfort and direction from a local NWFA (National Wood Flooring Association) Certified Wood Flooring Installer/Refinisher. The amount you will SAVE by having your floors REFINISHED will be worth the extra cost you will pay to have an NWFA Pro on the job. www.nwfa.org They are extremely good. And I bet dollars to doughnuts they have heard of 'your guy' and his/her ugly fixes.