I guess you already know that Apache itself will handle all the SSL bit for you, so from the point of view of Perl, you just need to write a "standard" CGI application.

Obviously, take a look at the CGI modules, you probably also want to take a look at HTML::Template

I'm not sure what your e-commerce app will do exactly, but if it's some shopping cart type affair, I'm sure there are lots of pointers in building those in Perl, as well as ways of linking them to online payment providers like Worldpay etc.

HTH,
--Loki