I'll agree with ProSource Memphis, you need to install an engineered wood floor because of the concrete. For our customers that are in your exact situation we offer engineered products, prefinished and unfinished (site sanded/finished), that have 3-5 mm wear layers. Some of these products can withstand 2-4 sandings, which equals way more lifespan than a cheap engineered floor. This equals less cost in the long run, but higher cost up front. Basically the thicker the wear layer, the better chance your engineered floor will last longer (80 years + estimated for 4-5mm), and the more expensive it will be. ProSource is correct, gluing a 3/4" solid floor down can be problematic and not worth the risk. Especially when there are high quality engineered floors that offer essentially the same thing. Engineered is going to be more stable with your fluctuating climate as well. You'll want a hygrometer in the home to monitor relative humidity. It should be somewhere around 30-60% RH for the floor to play nice. There are so many more variables involved in this discussion that entire books can probably be written. But that's my $.02

Hello Tom, It's a good one and means I can't vote as I have a Jackboot in both camps! (which you haven't allowed for) Paint is soo fantastic and I tend to think colour rather than white..but... that's only because I have had white floors for 10 years.. so need a change... Stain is gr8 if you want to go dark and have a grainy feel... Dark wood paint too is fantastic.. especially electric blue and other wonderments... So it really does depend on the aesthetic preference and what else is happening in the room... : ))

If they are real hard wood (or even a very thick engineered) you would probably be able to sand them down and re-varnish (depending if, or how many times it had been done before and their general condition). A decent flooring company would be able to give you a good opinion. I've sanded a lot of floors and they have always turned out well, just take care picking the colour of the final varnish as I've found that they tend to be quite orangey.

Where is the project ? I know some great fitters that could do this for you.