~I use Wings3D for my basic modeling (it's a free program, easy to use) After the initial "visual" model has been created I export it over to 3ds Max 8 to finish the pivot points, hierarchy (linking) and texture mapping it.
~The poly count is 7000 (I believe) anything below 7000 will need NO collision meshes. Anything above will need collision meshes added (the collision meshes can't total over 1500) so the maximum total for a completed model (with collision meshes) is 20,000
~This PBY-5A is 1/12th scale (or 104" w.s.) at the moment....I might scale it up just a bit more...but I'll decide that in the end.
~Time frame?? I started this thread on the 27th (and started on the model the night before) but I only put in an hour or so each evening (more on the weekends possibly) then again there are days I can't touch the model.....I haven't opened the PBY file since Sunday. I would guess I'm only half done with a completed model at this point. Some modelers (dhk79) can easily whip out a complete model in a couple days...if not less. I always tend to get wrapped up in more scale details though.
As far as Rhino? There are other modelers on here that could give you better advice in that department (maxkop is a good one to ask)
Hope some of this information is useful.