Like many here, I tended to obsess a bit when looking for chips. After 10 years, here's my list:
Buy racks when you can, small numbers when you have to. As noted above, your price per chip will be lower.
Don't be a afraid to buy used chips, especially here. PFC members know how to treat their chips. If you don't see the chips you're looking for, post an ad asking. Someone might be ready to sell.
Don't jump at every sale, particularly if its over your budget. Even though you fear it will never happen, someone will eventually be selling exactly what you need.
Seek advice here on what you really need -- starting stacks, buy-ins, re-buys. There are real experts here to help, (
@BGinGA and others) and you can avoid the giant mistake of spending lots of cash on chips you later find you're not using.
Big sets sound good, but you might not need it. If you don't host large games and think you need 1,000 chips, see above first.
Buying from strangers. Very risky on e-bay, and maybe crazy on Craigslist. You can ask here if anyone here has past transactions with a seller you don't know.
After that, enjoy your chips, plan your build to have a few small games as you go along, and post lots of pics. The chips are out there. You just have to catch them on sale.