Where can I get info on Tanks that can be set up to fire? Are kits available? I s there competition with tanks? any video on tanks? Any special websites for tank battling?

This is probably the most 'destructive' tank battling using paintball shooters inside 6th scale tanks:

http://www.rctankcombat.com/

All of these are custom, surely because of the liability issue, however there are smaller scales that shoot plastic BB like HengLong, Muari, Academy.