that depends on your timeline, when you get married etc. You can stay 90 days on visa exemption before you have to leave Thailand. (60 + 30 day extension).
I would personally make sure to have a cancellable /refundable ticket out of Thailand within 60 days of entering. You are also supposed to carry 20k baht equivalent of cash. Though its rarely checked, but officially a requirement.
Also make sure to be able to show documentation of your first few nights of accommodation.