I think you might be able to get 30 signatures! I went in March for 4 nights/5 days and we managed to get 25 and we only went to one character meal

we also missed out the characters in the hotel in the morning and those who come out in the Studios!
I'm not too sure on this, but I think that you can ask at City Hall for a birthday sticker? The Cast Members and characters are good at noticing those

you could have a birthday cake when you go for a meal too!
Have fun!