1) however much you want, just keep it from getting to deep. I've used 1-2 lbs/gallon for most of my tanks and it works out. 1 is on the thin side and 2 is just about right. If it comes in 50 lb bags about 4-5 bags should do the trick.
2) If you really freak the rays out they might stir some up.
3) No, this isn't really the best style of filter anyways. Get some canisters.
4) Just skim it over the top, way easier than gravel.
This is the planted section, so I'm not sure if you're talking about for a planted tank. If you are, then the pros go up to "Helps rooted plants grow easier". A canister filter will be best for a planted tank as you will have less outgassing of CO2 (good for plants)
In regards to bare-bottom, we should change that to "when in doubt, just leave it a big, water-filled, glass box that has no personality at all so we don't have to work as hard at cleaning it". I think that sums up bare-bottom nicely.