OSPF is a must in every modern network, especially if you have many pppoe conentrators (on every AP), unless you want to distribute routes by your self
, besides that close your backbone network (make it round) turn ospf on and be happy with redundancy and some sort of LB
After that there's just at least two different gateways to outside world (from different isps) at different points in your backbone, turn on BGP between them, and be really happy, since then you can think about your self as an excellent ISP:)
cheers
Michal