Any farms with mobs going through portal is not allowed
Nether roof might be allowed, since the nether roof has been used a lot in 1.17 CM

1. No they are not allowed.
2. Yes, but you cannot break bedrock. For example the ladder and epearl trick is fine, or get a tp from someone willing to tp you up there. Beware, they might just be doing it to kill you tho.
3. We have always been a pure vanilla server that hasn't used paper/spigot. Lag typically improves once people have settled more and aren't loading brand new chunks as frequently.

You can check out our rules Here that answer some of these questions.