1) There are many variables depending on the manufacturer of the rings and bases. I like my scopes as low as possible, but with clearance so it doesn't touch the barrel. You should be able to get height dimensions for the rings and base from the manufacturer and use them to figure out what rings will give your enough clearance.
I would only shim the bases if needed to align the two scope rings. I would not shim to gain clearance of the scope.
2) That would depend on your intended use of the gun. Obviously 24X will give you better X-hair positioning on the target then 9X will.
3) Its a nice kit, a bit pricey. Personally I use a piece of 1" bar stock and valve grinding compound for aligning and lapping rings, cost me around $10.00.
Good luck, Tony