You will rarely have to feed rabbits to an Imperator, especially a male. Over the past 25+ years of keeping Boas I don't recall ever feeding rabbits to them. (did feed Guinea Pigs and small chickens occasionally).

Regarding feeding schedule I mix it up with varying feeding rather than feeding on a set schedule. I usually feed anywhere from every 5 days up to every 3 weeks. (usually the feedings span around 2 weeks between feedings). If you want to go with a set schedule going 10-14 days between meals is a good set point to go with.

Regarding how big males get, they tend to stay smaller than females, but can and will grow to a fairly large size, I believe Gios male is approximately 7' and he's a good example of a well kept adult male and his potential size.