You want to go part or full time?
I'm a part timer for now. Maybe in a few years when experience and name grows I'll think different. Only made sense, cause I have a great full time w/benefits night job.
I work with a 2001 F-350 PSD 4x4. Chipper is a brush bandit 90xp (65hp w/winch) 1996, factory reburbished in 2004, nice shape cost me $7,700. Truck is my daily driver. I live on 90+acres so dumping's no prob. Nor was justifing a chipper, or all the other new toys, I mean gear, to use at home when jobs are slow.
When looking at a chipper, I would look at your local dumping situation and how many people are going to be feeding it. Some dumps take only chips for free. If so, and/or you're gonna have a few people feeding it, I'd go with a strong 100hp+ 12" chipper (w/winch). If like me, people are always looking for wood to burn and/or dumping blocked wood is no problem, and it's usually me and one other some times go for a 9" (at least 65hp) or smaller 12" (at least 80hp). I noticed when looking for chippers was the weight goes up real quick the bigger you go. My 90 weighs a bit over 4000lbs, perfect w/4 yards of chips in the bed. Yea, 4 yards ain't much, but it does equal about 4-5 loads of brush and I'm not far to dump it. Also, I'd try and get a chipper with an auto feed system that stop feed when rpms drop. You do not have to pay attention to the chipper so much and if you're buying used and it does not have an auto feed you do not know how many times they previous owner may have bogged it down hard or even stopped it dead while feeding.
Good Luck