just so i understand correctly, you're wondering how many fans you can run off a second ps? if so, that won't be an issue, unless you have both a LOT of fans in your system and a wimpy ps you shouldn't need a second ps only for fans. I think some of the large 120mm fans will pull close to 5watts, to give you a rough idea of the power draw you're looking at.
A couple of things here, first off, I wouldn't recommend using the molex plugs that come with fans, you only have the option of 12V or whatever speed control is built into the fan. my advice would be to invest in a fanbus (either with switches or potentiometers, whatever suits your fancy), or build one yourself if you're into that sort of thing. that way you'll have a lot more control over the noise and effectiveness of the fans in your system.
Here is a great link on the principles behind a fanbus. As far as installation basics go, take a look in the articles section here at procooling, there are a couple of good detailed articles about that. Rule of thumb, its better to have fans sucking hot air out of your case(negative pressure) than blowing cooler air in(positive pressure). your fans will be more effective that way. and last, when it comes to fan size, bigger is better. larger fans in general move a lot more air at lower rpm's, thus making less noise, also they make a lower-pitched noise that isn't as noticeable as opposed to small whiny fans. This has pretty much been based off my experience fooling around with my systems, I hope this isn't too basic for you, and it answers your questions.