Limit the guest-network (ports and speed)

Hi!

I would like to limit the guestnetwork a bit and was hoping to get some input on how. :)

I want to limit what ports the clients on the guestnetwork may access (TCP 80/443/25/110/143 and UDP 53) - all others should be blocked.
I guess this could be accomplished by iptables, but I'm quite new at iptables and not quite sure how to do it...

Also, is it possible to limit the bandwith for the guestnetwork (either pr client or the network in total)?

Btw, running the newest Merlin on my 68U