fishing contest gives 1000 coins to person who comes first, right? so, can two accounts with same ip address, or in other words, multiple accounts. can two accounts which have same ip address or multis can participate? that means, i and my other account, both can participate and win the fishing contest?

I don't think you could do that. Same as daily raffle, you're not aloud using multiple accounts in Daily Raffle.

you are not sure? if i do that, there is a chance i may get banned, so i thought i should ask first, but, it looks like i have to try it to know. what else can multiple accounts not do? i know some, they are
1.) Can't be in same clan.
2.) Can't claim more than 2 of same promos(although they can claim both promo of double promo each)
3.) They can't bid on their own pokemon using other account in the auction house.
4.) They can't hold auctions together.
5.) They can't bid together.
Anything else I am missing here in this short list?

1. no, you can be in same clan
2. yes
3. yes
4. I don't think so
5. no, if you not bidding in your poke, then that's not a problem