I think what you are referring to as 'intermediate ceiling joists' are what I would call hanging beams. They're there to hold up the ceiling. I'm pretty sure that they don't need any tie-down, just skew nailing. Anyway, a triple grip at each end wont hurt. We used cyclone straps on all of our trusses because it gets a bit windy where we are building. Triple grips would have been enough to satisfy local regs though.
Hope you're going to put lintels over the openings in the back wall. I think I would have preferred to have a ribbon plate on that wall too.
"I don't practice what I preach because I'm not the kind of person I'm preaching to."