WiFi shared throughout a small business park. Paid internet service. Help (please) to think about how ?

I have an office on a small business park, it's probably 400m long by 200m wide. There are lots of small units. Some of the units do not have Internet or even a phone line. I was thinking I could create a paid internet Service for the business park. Maybe at a small cost of £2 per day or £30 per month.

I can get a nice 300Mb Virgin line in my office and share that out. I want to have each customer who uses the services only be able to "see" their computers, as it needs to be secure so Bill in unit B can't see Jane's computers in Unit C.

I came across the WAP371 from Cisco, these allow up to 8 SSIDs to be broadcast, with different Vlans per SSID too! With these in mind I could separate the SSID's per customer. Tell Bill to connect to Wifi1 and Jane to connect to wifi2 etc.

Then have each vlan going out to the WWW.

So it'd look like this. Note: I'd try and have the CPE and router the same device if the ISP will allow.

WWW > CPE > Router (seperating Vlans, controlling DHCP) > POE Switch > Cables going to different WAP's around business park (or a cabled connection to a customer who needs/wants a cabled connection.

I was planning on having a UPS to keep the network up if there is a power cut. I was planning too, a 2nd internet connection (different ISP) for a backup. Each connection would be limited and split evenly. So If I had a 300 Mb line into my office I'd have 30Mb down (based on 10 customers) What would be the best way to separate the bandwidth to individual vlans?

Another thought... I was also thinking about having an added service to that as a storage service. So they could rent 10GB for example from me for a backup. I was trying to think of a way to do this without having to buy 10 NAS devices, I'd really only like 1 NAS device but I can't think of a way to do that. Any ideas?

Oh and I'd need some sort of payment gateway, so the customers are blocked to getting to the internet unless they have a token for today / the month. I've been looking for a gateway like that in the open source market, but I'm not coming across anything that says it does the above.

Thoughts on the idea?