I am also in the same boat. First time airbnb lister, but struggling to get committment from guests. Its a lot of money and I'm happy to take a deposit, but there is no option on airbnb. A deposit option which first allows the host to chose the % of deposit and then stipulate the date in which full payment must be received following communication and agreement with the guest would be a very very worthy feature in deed.
I can't image this subject is new, but is simply being ignored by the airbnb mods.
Has anyone else attempted the earlier posts suggestion of asking for booking and payment for say 1 week of a 4 week request, then agreeing with the guest when they will book and pay the remaining 3 weeks?? Would be interested to know if this works.