you wouldnt need the P2P shield if your not using a P2P (aka peer to peer) program such as limewire, kazaa, etc, but I don’t think it will take up any extra resources (although i could be wrong). I think it would be a good idea to leave both web scanners on, but if u think it is slowing your computer too much you might want to change them to normal instead of high settings.

All of the following firewalls seem to work well with avast, but i am sure that there are others that are compatable as well: zone alarm free, comodo, Pc Tools firewall.