A pre-chiller is pretty much useless IMO. If you want to chill stuff better than your tap water, buy a cheap submersible fountain pump and use that to pump ice water through your chiller instead of straight tap water.
Generally speaking the bigger chiller you have, the faster it cools your wort, so long as it's not so big that it's not covered by wort. For smaller 3-5 gallons of wort a 25-50ft chiller is sort of standard, but you have to be careful about the diameter of the tubing used. You want at least 3/8" ID, but better if you can get 1/2". There are some rather shady businesses selling wort chillers that LOOK like a great deal until you get it and find out it's 1/4" tubing and tiny.
Usually the best deal is to make your own. It is not hard, you just need something round of approximately the right size to wind the tubing around to make a spiral. Leave some straight tubing at each end so that the ends will stick up out of the pot, and you can attach vinyl or silicone tubing to them with hose clamps. If you are somewhat handy, it's not hard to sweat some pipe fittings on there and make it nicer, but for basic use hose clamps work fine.
Then you just need a way to attach it to your water source, whatever that may be.