Ubuntu – UFW on Ubuntu to Allow All Traffic on LAN

1-2 .Theoretically as many as you like.Practically you'd first start observing some memory issues because all these rules have to be loaded. Then you'd get to the real trouble of maxing out your CPU's because you'd have to check all these rules until you hit the one that matches. Also depends on what you are logging (i.e. are you logging everything, all DROP's,and so on?)

3.Use IP sets, block whole ip blocks and/or combine with hardware firewall.

4.I am not familiar with bbPress but there's a bunch of things that you can do to mitigate attacks, from caching to pre-blocking related ip blocks to the botnet.

Reload the service sudo ufw reload and sudo service iptables restart, Remember to allow ssh if you are on a server.