Yes, you need to check in to get your Artist Alley (AA) badge.
Your table can be open any time the dealers hall is. Your table can not be open when the dealer's hall is closed.
Yes, and Yes. Your table location is planned in advance.
Can't help you with the last one, I've never run a dealer's table.
If you have any more questions please e-mail
admin@mewcon.com or PM Admin
here.P.S. There is also more information in the wall of text
here.