Accepting Credit cards is a major decision with E commerce projects, but is not well understood.
Scenarios include...
a... DONATION MODEL : taking small payments for non-profits
b... SUBSCRIPTION MODEL: AKA the Dating site model, the user pays a monthly fee for access.
c... SHOPPING CART:
Other considerations...
a... hosting environment ( multi tennant, aka shared hosting usually does not qualify)
b... Shopping Carts ( DRUPAL COMMERCE, DRUPAL UBERCART, MAGENTO )
c... PayPal solutions.
A very good starting point is to study PCI compliance rules.