questions about online shop integration

hey guys,

be warned: this is a completely offtopic, non-wpmu realted question but I knwo we have a lot of people with vast knowledge around here so here is the question:

I am looking at building/implementing my first web shop.
Its going to be a small project, it won't be a huge web shop, so I was looking at building it on top of wordpress with one of these two plugins: http://wordpress.org/extend/plugins/eshop/ or http://www.instinct.co.nz/e-commerce/

My problem is I haven't ever dealt with online payments.

I see that the first plugin supports Paypal, Payson, eProcessingNetwork, Webtopay and Cash/Cheque while the second one supports Google Checkout, Paypal, Authorize.net, Payment Express and many other trusted payment processors.

I am not really sure what the difference between these "providers" are, except of course their exact offer, the percentage they take, the costs etc.

What would one look at when chosing one? Does it matter at what target the web shop is aimed at?

I.E. the project I am talking about is aimed at south african citizens, meaning I am interested in offering payment by credit card VISA and MASTER card. can I chose any of the payment gateways lsited above that offer support for these two types of cards?

Any other hints/links/tips for me? I know I really need to do some serious reading but am unsure where to start.