I would like a way to run many URLs without having to use a unique IP address for each site; such that it would use the URL and as a lookup and only have one IP address per server
Yes you can use one IP for numerous domains hosted in ISPConfig.
In your IP Pool you can define your IP's available for use, you could have a pool of let's say 2 IP addresses- one address might only serve your ISP site and services.
The second IP in the pool can be used for all clients you sell hosting to, just define the clients domain.tld name and then the IP address intended for clients and that's it.
Hope this helps