In general, you do not want to handle credit card information at all, not even in a pass-through capacity, if you can avoid it. Check to see if your payment gateway supports "transparent redirect" (and which ecommerce systems they know of that've integrated with it). This will make your life about 500x easier in the long run.
If yours doesn't, my favoritest is
Braintree, but there's probably others out there too.
I don't generally work with ecommerce systems, so I'm not sure what's considered "good" nowadays. I always underestimate the resources required for PHP applications in general, but ecommerce systems seem particularly rotund. (I dunno, maybe it's the sales tax tables.)
_________________
Code:
/* TODO: need to add signature to posts */