Hi

Is it a good idea to provide 3 different shipping company for buyers when they check out ?EX: ups, fedex and USPS

Sure, the more options your customers have, the better. If they see that your company can ship their parcel many different ways, they will value that, and most probably remember that and maybe tell their friends about it. For example, Zen Cart has quite a lot of shipping modules, but you need to install them manually, and Avactis shopping cart has 7 shipping methods in the base install. It's not enough to setup the cart though; you usually need to register/setup at the shippers themselves.

What kinda of account I should Sign up for each carrier? Aslo, Do i have to pay for any fees if i dont ship out any packages?