using Range of ports on a virtual server with/without using iRules

You can create a VIP that listens on an IP and any port (wildcard), but you can't create multiple VIPs with the same destination IP and wildcard port. You have a few options though:

Create a single VIP with destination IP and wildcard port and use an iRule to pool to resources based on requested port. You could also optionally give each customer a different DNS name to the VIP and load balance based on that.

Create a separate IP and wildcard port VIP for each customer (a different IP address for each). You can then optionally limit access based on the defined ports.