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Of course, right after I say I'm busy I wind up with free time...
1) It takes approximately 920 g of filament for the whole machine, so one roll ought to cover it. Spreadsheet attached if you're curious. This is using 15% infill, 0.4 mm nozzle, 3 perimeters, and 4 layers top/bottom, which is what we used for our prototype, your mileage may vary.
2) Covered!
3) If you just get everything through Amazon, buying all the machine screws in the 100 packs and whatnot,the total comes out to about $350, not including shipping, those hundred-packs do definitely add up... I'd definitely look at local stores to see if they sell screws à-la-carte, or try to find a 'misc' collection of M3 machine screws, updated spreadsheet with calculations added for your convenience.