Welcome aboard silent35 - those are all good questions!
I'm away from my compressor at the moment but if I remember correctly it's only about 2hp. Ultimately it's not so much the power, but rather the size of the storage tank that is important (although in practice the two work together). You see a bigger storage tank means that more air can be kept under pressure which is available for immediate transfer into your pressure pot. If the storage tank isn't big enough then the compressor needs to be powerful enough to deliver the extra air required very quickly.
I'm sure that there are some nice calculations that could be performed to work out the optimums, but sometimes plain old "this will work" is better
The compressor I'm currently using is just a cheap no-name one very similar to the following: . A full tank will easily fill my 10L pressure pot to 55PSI, although near the end the compressor will cut in again to top itself up. And that's under AU$90!
I wouldn't go under the 2hp mark, and with a price like that above there is really no need to. Actually, more of the expense is in setting up all of the fittings and hoses!
I've always used oil lubricated compressors and have never had a problem with the silicone or resin. I'm sure it can't hurt to run an oil filter and water trap, but I don't have either (it's on the list of "one day" things to do). It may in fact come down to the specific brand of silicone and resin - I know some silicones can certainly be more sensitive than others.
Hope this helps!
Oh yeah I can make that....