Personally, I don't think centralized recording in feasible. You're putting too much faith in the continuous availability of your Internet connection. Every time there is an issue (slow credit card verifications, slow POS, etc.) everyone is going to want to blame the camera system first. Since you don't have an IT department, I think you're setting yourself up for trouble.
Port forwarding is not difficult really, it's the standard approach used almost everywhere. You could save yourself a little hassle by setting up a simple VPN server at your HQ and a VPN router at each remote site, but even that isn't really neccessary.
IMO your best approach is an NVR appliance at each location. There are options available from all the "big names" as well as some better DIY options. I'll refrain from recommending anything specific out of personal bias ;)
One question that I didn't see anyone else ask... What do you want to *see* with this system? Store overview? Ability to see details of currency at the POS stations? Something else? Will all the cameras be in the store or are any going to be mounted outside covering rear doors, dumpsters, etc.?
