How to set up iRules to create a generic site that will distribute to multiple servers/pools

The best way to do what you're looking for is by using the APM module, but that would need to be licensed for use.

The other option is one we've used a little bit, which it to do custom rewriting to the response. Since you're using URI based routing instead of HOSTNAME routing, you'll need to rewrite the response to ensure the prefix exists on all urls to that same site (e.g. for accounting, every link URI should start with "/accounting/xxx"). If your backend server already has the site set up to use /prefix/xxx, then the rewriting would be minimal if any at all.

Another option as part of this would be to use a little fuzzy logic with the Referer header. You could check to see if the uri part is prefixed by one of your routes and redirect the user to a uri with that prefix. The problem with this method is that it's not foolproof, so it may take a bit of work to accomplish. (Took me a while to build out for our environment). I can probably share some logic if you're interested.

If you can use different hosts (e.g. acct.xxx.com or email.xxx.com), even if they point to the same IP address, you could use the host header to then route the traffic to the desired pool (or other virtual)