Questions about peer2peer filtering

I read that if p2p traffic goes through an encrypted connection there is nothing to be done so lets assume it is not.

I also assume only allowing outgoing connections to remote ports 80,443 would be a good enough stumbling stept assuming those clever enough to connect to p2p services via these 2 ports would also be clever enough to use encryption, right?

I see that lede has iptables-mod-ipp2p, kmod-ipt-ipp2p and l7-protocols - how would one use those to block p2p traffic or NNTP traffic?

just looking for some hints and links, I'm not all that well-read about iptables, currently busy learning more.

What I am trying to do is secure a more or less public wifi network in an area where data bundles are pretty expensive from (too much) abuse.