iRule - newbie question

1a. If you're going to use HTTP-based iRules you must have an HTTP profile applied.

1b. Considering that you're directing traffic to specific HTTP (port 80) and HTTPS (port 443) pools, then yes you should enable port translation, but it probably wouldn't hurt either way.

2a. The important aspect of this configuration is that you're doing HTTP and HTTPS on the same VIP. It would be easier to use separate port 80 and port 443 VIPs with the same IP address. In a single VIP config, however, you need to be able to turn the client and server SSL profiles on or off based on the client request. Something like this should work:

when CLIENT_ACCEPTED {
    if { [TCP::local_port] == 80 } {
        SSL::disable clientside
        SSL::disable serverside

         URI pool selection logic
        if { [string tolower [HTTP::uri] starts_with "/foo" } {
            pool Http_Pool_A
        } elseif { [string tolower [HTTP::uri]] starts_with "/bar" } {
            pool Http_Pool_B
        }
    } elseif { [TCP::local_port] == 443 } {
         URI pool selection logic
        if { [string tolower [HTTP::uri]] starts_with "/sslfoo" } {
            pool Https_Pool_A
        } elseif { [string tolower [HTTP::uri]] starts_with "/sslbar" } {
            pool Https_Pool_B
        }
    } else {
         drop everything else
        discard
    }
}

With this iRule applied, you'll also want to set a client and server SSL profile on the VIP by default. When it encounters a port 80 request it'll turn them both off.

2b. I think the above iRule covers that.

2c. I think the above (single) iRule covers that too.

3. Create your 4 pools and assign them their own individual monitors. The BIG-IP will handle the rest naturally.