Yes, you are able to transfer everything from one account to the other.(except for starters of course) You are able to mail items from one account to the other which costs a lot depending on how many items you are planning on transferring. The two window method will not work however, I'm not completely sure if running PokeMMO on two different computers would allow you to trade between accounts and yes, you are able to sell the EXP Share on the GTL and transfer the money to your other account and no, you will not get banned as you are allowed to have an unlimited number of accounts.
1. You are able to create as many accounts as you want.
2. It is not a problem to have more than 1 forum account(not that I know of)
3. You are allowed to download and use roms but forums cant supply you with any.
4. Yes, mods from the Client Customization can be downloaded without any consequence.
5. If you have the character on the same account, trading is not possible, otherwise, you are able to transfer everything(except starters) from one account to another.
6. There has been wipes in the past but no one knows except for the Admins if any more sweeps are soon to come.