As far as payment processors go, you likely already have yours in place. PayPal.
PayPal is the main payment processor in the entire online world.
Sure, there are others, and many are pretty good, and those are fine to set up an account with just in case you get a buyer who lives in a country that PayPal does not support... But those are actually few and far between, so you absolutely want PayPal as your main processor.
On the other hand, if you live in a country that PayPal doesn't support, then you are going to be forced to use an alternative provider.
So if this is the case for you, just do a search for "PayPal alternative" and you'll get a good number of alternates and should pretty easily find one that supports your country.
Your sales volume will be lower when you do not have PayPal as your primary option. It is still worth it, you just won't make as many sales because people like me tend to "move on" if an offer does not provide a PayPal option.