It is hard to get a straight edge on a very long board using just a joiner; if the board is bowed you can tack on a perfectly straight 'guide' board on the piece of flooring and the guide board up against the fence of a table saw will cut off all the waves.
It is hard to take the curve out of a wide piece of stock by just clamping, wedging and nailing it into submission. The wood will fight it's way into it's natural curve after a period of time. Get that sucker straight before nailing it down.

Before running any of that flooring through a planer consider not only hidden nails that will nick your blades but also lots of little bits of grit and pebbles that are embedded in the wood from years of walking on it. Also the heat from the planer blades will want to melt some of that varnish and it will gum up everything in the planer; drive rollers, blades etc....
I would first belt sand the surface a little just give the varnish a rough texture so the drive rollers can get a grip. Take just a little off at a time as not to build up too much heat resulting in scorched wood or the previous mentioned varnish melting. 1/32" to 1/64"
The bigger and heavier the planer the better.

I have done a lot of floors and I would recommend getting a recent book from lowe's, home depot on how to go about this project. If you start ripping up the floor you might find the wood is awfully brittle, so you may have to stop and re-evaluate your entire project and methodology.
( For years I owned a custom woodworking and cabinet shop and my Dad was a Woodshop/cabinetmaking teacher)

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