I am not sure that people would want tintypes for their wedding photos. They look nice but they have an antiquated, gritty look which might not be suitable to happy occasions.
I would suggest going for colour film mainly. The reason is that it is harder to emulate digitally than B&W. Most customers would not see the difference betwen a dgital shot processed well i Silver Efex and the real thing.
But with colour film you could give them a unique look which they couldn't have with digital. Presumably, it would be more expensive though due to the extra work, but if you use really good portfolio samples, I am sure people would go fo it.