Re-balls - In this country that I know of - Planet eclipse, Just Paintball or Tomahawk boomerang reballs which are sold by Warped Paintball.
I havn't seen a 3000psi fibre wrapped bottle for a long time. If you have the money go for 4500/5000psi fibre wrapped bottles. If not look around the place speak to a few trade companies if you are setting up a company. If not try and buy all your main stuff from 1 supplier like just paintball or planet etc then you will get a better discount.
Compressors - if you do want to go ahead and get a compressor look at ebay under the section dive compressors I know there is 3 or 4 on there at the min. BUT BEWARNED if you buy a second hand one you better know someone with mechanical and im talking good mechanical experience. You will also need a qualified electician to install it. A lot are 3 phase which your house wont have so you would need a single to 3 phase converter.
Insurance if you plan on charging even a penny I would suggest insurance try someone like leisureinsure. Though in my opinion I would have insurance full stop, this country is turning into an american culture on sueing people.