Lastly, regarding broadband usage, if I do use LAN for gaming, does it use less bandwidth compared to playing wireless?

We're on the 30GB Vodafone Ultimate BB Deal and seem to use 30GB within 15 days. There are 5 family members that use the internet on a daily basis but I think I use the most broadband usage.

Your wireless is still on the LAN, so that won't make any difference :)

My earlier comment about disabling DHCP/NAT etc was assuming you were connecting the two routers using cat5, not having both connected to the phone line.