Shopping carts questions

[trig]

My local bank has provided me a merchant account.
Now, all I need is a shopping cart -- which I know nothing about.

A few ?'s:

1. Can a shopping cart provider suddenly freeze your money?
2. Do shopping cart providers really care what you sell?
3. Do shopping cart providers really care that I sell 20-40k a month?
4. I want to set it up to where all I have to do is send my website guy some html code so he can plug it in to the already existing 'buy' button to redirect my buyers to a different place rather than ccnow.

I like ccnow, but it takes way to long to get paid.

thanks in advance.