I would strongly suggest you start out with only PayPal as opposed to 2checkout. Mainly because, PayPal is infinitely cheaper in terms of fees. If you start with PayPal, the sooner you'll be able to afford a merchant account (because you won't be paying high commissions on sales), which isn't so difficult to obtain these days anyhow with so much online business.
There are major online retailers who rely solely on PayPal as their shopping cart.
I strongly suggest you skip CCNow and 2Checkout if you can help it. 10% is vampirism. ....is that a word?
They each juggle their numbers differently, but it comes out pretty much the same, and is waaaaay expensive. If you can avoid them at all, you'll save money you could be putting back into your business instead of their pockets.
Also, when you're ready for it (with a merchant account) look into Mal's-E for your shopping cart which has a built-in PayPal payment option for your customers. I just switched and my sales have doubled.