Small store infrastructure - where to begin? [closed]

All separate services...

Your point-of-sale vendor will help you with requirements for the POS solution, and may provide the hardware.

Security systems are usually discrete and the vendor you use for that will probably bring a DVR solution. Consider IP cameras for flexibility.

PC's are PC's... A good local tech can help you there. Think about mail, web hosting and other internet-facing services. Possibly outsource those. (assuming you'll do the web design)

You haven't really provided much of a case for Linux, based on what I hear. It won't necessarily keep costs down... Maybe a Microsoft Small Business Server is worth a look.

If you only need file sharing and/or backups, I consider a better deal to use a NAS solution (look up drobo). This is much simpler than a full server

You need to step back and sort out exactly what functions you need before you worry too much about how to back "stuff" up.

I'm only familiar with grocery and coffee shop POS systems, but I'm sure there are many suppliers you can choose from for your needs. I wouldn't plan on buying your own generic PC for it until you talk to some suppliers, they'll tell you what to get and/or sell it to you. If you're checking local suppliers, don't forget to call cash register dealers.

Hosted email would be the way to go at the scale you're talking about, Google Apps would be an easy starting point.

Since your users are used to Windows apps, you could start by just using a desktop and sharing a couple folders on it. I don't think a NAS box would be any easier for them to use. Backups can be syncing the data to at least a couple external drives.