While I somewhat agree with the above post, it is not legal in NB to tow 3000+ without brakes. In fact his example requires brakes on both axles.
The OP is correct that he will have at least 7500 lbs behind him and yes I would do it BUT only with a Allison 3000 tranny and not before improving the hitch and putting a air operated braking system on the F150. I would also keep the MH weights down.
Interesting that the OP will not tell which different "bus" he's looking at that has the same HP as what he already has. Doubt we will hear back from him. I've learned to not waist my time on new members with just one post... He had two.