In my opinion trade servers aren't really ment to be fair. Their trade servers if you play on them that's just you playing on them. Not really a main intention (although I know most people on it do me included) And I think the absence of a bunch of rules might be what makes it fun.
But I also understand having to at least have a few guide lines... and with that said I don't mine any of those EXCEPT!!!!!!!!!..........
Number 2.
Engies sentry hopping to the other side of the nether
That's part of TF2 as a game in general. I don't see anything wrong with this at all, its no different then a solider rocket jumping.
But the other 1, and 3 rules I understand.