Central Database, Multiple Shop Fronts, Annual Membership

Shopping Cart solution required, with central database and 5 different shop fronts. I run several BBQ web sites and have decided it is time to add shops to them. Some of the sites are wordpress and others are Microsoft Expression, I will need the system to work with both and be integrated to paypal. I need the database to be able to offer a discount to membership so part of this project will need to be a rolling membership system which auto bills after 12 months. Look and feel of each shop front must match current sites.