Good morning,
Please let me know if there are any spaces available/left for a walking tour at* the museum tomorrow. If so, I'd like to know at what time and how much it is going to cost/it'll cost.
I also would like to know if I have to book the tickets right now or if I can buy them tomorrow, just before the tour starts.
*Lo que tú habías puesto "to" no es que no tuviera sentido sino que pensé lo que realmente querías decir era "at."