I can install, configure & support the following:
This can be located on your premises, or I can arrange hosting at several ISPs.
OpenBSD makes a sound foundation for running a web server. It has a great security track record and unless you are trying to run a site like amazon, more than fast enough even on moderate hardware.
Apache is the most widely used web server on the internet, and has been since 1996. On OpenBSD it is run in a chroot by default to further improve security.
osCommerce is a PHP-based shopping cart. It is very popular because it is easy to setup & maintain. osCommerce supports a large number of payment methods.
SQL-Ledger< is a web-based double entry bookkeeping package, which supports multiple users and multiple companies.