WISP Best Practices??

I have been placed in charge of network administration for a WISP. A lil background: the wisp was previously a wide-area-broadcast network. I have finally got the network routed with ospf and the next lvl is scalability. My goal is to have a central device that handles out LIVE IP addresses to end user routers/pc’s. My problem to over-come is the fact that for billing purposes we need to know how many devices end users have connected because the price is based on the number of client devices… I am thinking set up authentication such as PPPoE (maybe something else), that will force users with more than one computer to use a router that we manager. I am thinking this will solve the billing issue of knowing how many devices a customer has connected to the internet, and regulate the number of LIVE IPs that get handed out. Does anyone have some advice.

if your customer use a simple router , you cannot see the devices it masks: they coud be 1 or 1000!

I dont know solutions to this.

Well I think I have made it clear that bandwidth tiering for billing is the only viable solution. What do you guys/ladies see as the best practice for managing a limited number of live ip addresses to customers from a central location? EoIP tunneling to the AP router maybe? I am going to test this scenario and see how it works out.