questions about electric fans.

I am looking to upgrade to electric fans for my nova. there going to be going on my stock radiator since it works excellent and i had a few questions before i go any further on it

how much of a cfm fan should i be looking for?

one or two fans?

do i need a fan shroud?

what other things do i have to buy for it? (to wire it up)

can i wire it in with a stock intake?

where do you buy the switches that come on at a certain temperature?

can you change the temperature at which they come on or is it a set temp?