This one may be elementary, but... I think it would be advisable to sister the joists under my tub, for no other reason than "better safe than sorry". I really do feel pretty comfortable with the weight bearing capabilities of this structure, but.... How far out do the sister joists running parallel w/the originals need to extend beyond the tub footprint? For the perpendicular supports, just toenail them to the original joists?
I really appreciate all the help you all are giving me. Wish I had discovered this forum in November!! Almost done now!