Insulation goes under the floor, between the joists, so forget about the cork, etc. I would put down red rosin paper first to minimize squeaks. Forget about air spaces, etc. Also, I would snap chalk lines on the paper (after it was stapled down) to mark where your joists are and use nails long enough to get down into the joists. If you don't then it is a recipe for a squeaky floor. If the doors are too low then that is a separate issue - It just takes a few minutes to take a door down, put it on some saw horses and trim off some of the bottom. If you do cut your doors don't forget to seal the bottom edge with primer or sealer or else your doors could swell and/or warp. You should DEFINITELY get a special dovetail saw with an offset reversible handle (they have them at Home Despot) that you use to cut off all the bottoms of your door casings so you don't need to cope around them. Just take a scrap of your flooring and rest it down on the floor, against each casing - then this saw rests flat on it and saws off the bottom of the casing right at the level of your new floor. THen your flooring slips right under.
Other tips: - I would "ease" the top corners of each board with a chisel so they aren't sharp. They will wear less that way. - If you want to stain it use minwax "wood conditioner" first according to the instructions, to reduce pine's tendency to have dark blotches here and there. - I always use oil based poly for hardest finish. At least 3 coats - all but last one high gloss b/c it is the hardest. - Realize ahead of time that your floor will get dinged up, no matter what you do, and this is the "charm" of pine. THings that hurt = sand tracked in, gravel stuck in lug soles, high heels, dog claws, kid's toys.