You might want to look more deeply at the ecommerce package, depending on how certain you are at expanding.
dekkasupply.com uses ecommerce package, but we've switched off the payment-gateway aspects to use the free services by paypal, since their rates are cheaper than the ones we've been quoted by the payment-gateways! Generally, payment-gateways are supposed to have more competitive rates.. Anyway..we're working on a gateway to interface with Paypal Pro gateway, but finishing it is low priority at the moment. Other features are taking precedence.
The paypal procs are coded to use the existing ecommerce data, so we can toggle back and forth between services on the fly, when payment-gateway services are setup.
With the ecommerce package, you need to buy an SSL certificate, and pay monthly fees for a payment-gateway service which usually also quote the merchant-gateway pricing.
For few items or low volume, the overhead is not practical compared to services provided by paypal, google and other vendors promoting their cart services for free use.
ecommerce has lots of import facilities, so you can always choose something simple, and then upgrade later when you decide to go with OpenACS ecommerce package.