From what I've heard. tow companies can take hours to respond. We have never had to use our SeaTow membership (knock on wood!) but I've fished with people who have told me stories about long waits to get towed...
As far as bay boats offshore, We used to run our Kenner 21' up to 25 miles out of Port A, and I know at the old 19' mile rig out of Port A we have tied up beside a guide in a bay boat! During the summer be wary of thunderstorms, they can sneak up quick. The biggest danger you'll face is not wanting to bay fish anymore, leading to your bay boat getting traded up... good luck!