Thanks for the compliment, and for your feed back, it's much welcomed. As to how much sandpaper to buy, I didn't write about that because every floor (new or old) is different. In your case, a sheet of 36 grit should last about 200-300 square feet. You can tell when the paper is wearing out when you have to really push the machine to remove the "over-wood" on the newly installed floor. And generally speaking the finer grits will all go about as far. But buy more paper than you need . I'm sure they allow you to return unused sandpaper.
Be sure to sand with 36,60 (slowly as to take the coarse marks out) and then 80 and finally 100 or 120. Like I said in the article I don't buy the really fine paper preferring to burnish the 80 on the running machine. Nice Trick.
As to the stains, the easiest to use are the Minwax wood stain, especially for a light color like cherry. But, I still say to hire the pro to follow my sanding instructions, he's got the better machines. But most certainly do all the finishing of the floor yourself, that's the fun part anyway. If you think that the installation was tough, you will find the sanding about 10 times more difficult. Don't say that I didn't warn you.
Oh, and as to the finish, for sure 3 coats of oil poly applied just as I said in the article. Don't be tempted by the new industrial water based finishes (Street Shoe, Traffic) they will make your floor look like plastic. And all the water based finishes last only about 10 years before they turn opaque. I will do an extensive article on this very subject sometime this year. I've been talking to industrial chemists and art restorers, about the whitening of water based finishes. Big Problems. Hidden from the public.
For now I would say the brand of oil poly that I mention in the article has held up well in my household with the same sort of use (that your mention) for about 22 years now. Not bad.