Build website template for new product release with (paid) download section

The project is to build simple template-style website that can be quickly customized to promote a new product as well as offer registered members the ability to login to review/purchase specific products. This would include integrated payment modules that accept Stripe and Paypal. These modules should be easily re-usable across all products. Overall, the website (system) can be interconnected to re-use the same membership accounts, payment modules, etc, but ultimately -- the design of the layout will be such that the products "appear" to be completely independent of each other. For example -- our company currently offers 3 small software products -- we would like to quickly modify a set of 'professional' templates to reflect each individual product. Some manual file adjustments, links, filenames, etc, is acceptable. At this point, we don't necessarily need a CMS. We would just copy the modified files to our web-server and then maintain manually. Back end programming could be done in PHP or asp.net. A database, would be in mySql. We will provide a 3rd party hosting instance for final testing / release. Please submit samples of proposed layouts, as well as a detailed strategy to implement the back-end user-management and payment systems. Thanks.