Assuming you have enough experience in both the tree world and the business end of things here is my 2 bits. Contrary to a few suggestions I personally would never buy used gear period. Always buy industry standard stuff ie. MS 200T not some cheapo saw. Don't invest to much to fast it will give you time to learn whats needed and whats not. The basic gear would be all the climbing junk like saddle etc. should set you back a G note. You will need 1 climbing rope, 1 bull rope and a utility rope 1/2" is fine. A spool of 1" tubular webbing and a wack of Biners sport,locking and non locking that will be another G note. You will require a 1 ton dump truck( get this BEFORE some moron tries to sell you his piece of **** bucket truck) as you need to remove branches etc. and believe me hand bombing on and off the truck is bullchit! Don't bother with a chipper in the beginning it's not needed. You will need to secure a dump site for all the trees you will be killing try leasing a spot from a farmer don't use logging roads it gives tree workers a black eye! Insurance is a must don't play if you can't pay you will be screwed if something goes bad. Extra stuff that pays LARGE dividends are things like BIG SHOT, Silky saw, blocks and slings. I would say a guy could start from nothing and be logging in say....10 G's. The only thing I would buy used would be the Chevy 1 ton dumpy!
Then it's time to bust some ass and make some squirrels freak out like back in Nam baby!!!