Don't buy a used PC, pro shops work them hard until close to death then sell them for close to retail, but enough of a discount that they still sell fast on CL.
The HF isn't bad, and is cheap with coupon etc. good to learn on, then when you "need" more power look at other options and put a 3" backing plate on the HF and continue to use it for smaller areas.
Detailing can get expensive fast, good goop isn't cheap ala $30/quart, pads, backing plates, towels, cart to hold all the goops and toys, it adds up fast.
Hard to go wrong with Griots, nothing they make afaik isn't at least pretty good, but none of it is cheap.