Is it a requirement that we be in costume while we are at the booth. I ask this because I would like to sign up, for a slot but I will not be in costume all 4 days.
Not at all. There isn't any requirement to wear armor or even a TDH shirt while working the table. I think I'm the only person who has worn their armor all the time at a con and while working the table but that's just because I loved it.
It is entirely up to you whether you would like to be wearing a costume while working the table.