State of the Union guests

Louisiana Rep. Vance McAllister is inviting one of the Duck Dynasty guys to the State of the Union tonight:

That got me wondering, how are guest passes to the State of the Union allotted. Do all congresscritters get to invite guests, and if so how many? How many people does the gallery hold? And who typically gets invited to these things?

I think I saw Uhura-Nichell Nicolls.