Documentation for marriage visitor visa

Hi I've been reading lots of different threads and information and slightly confused as to what documentation is needed for marriage visitor visa. A bit of background - I'm a British citizen, partner is gambian, we had out nikkah in gambia and would prefer the legal ceremony here so my family can attend, my nan is end of life and cannot travel hence another reason to want a ceremony here also. My partner works and he can take leave to come here, he has children and lives on a compound with his family. Im a student and also full time carer for my son so do not work. We plan to spend the next year or 2 visiting each other and eventually plan to stay in gambia. I have recieved dates from the local register office for giving notice and for actual wedding which we will be booking next week. My mum will buying my partners return flight as a gift to us (can this be booked once visa is approved if we provide travel dates?) And I will be providing the financial support here as my partner did whilst I was in gambia. Any advice would be greatly appreciated. We hope for him to visit here in jan