That sounds pretty ugly. You'll want to talk to the inspector for sure,
cause nobody around here is going to come to any kind of consensus.
But, the usual idea is to try and get most of the plumbing on one side
of the house, so many of the pipes can be run basically in a single
wall, usually the back of the house. This makes the venting easy.
Yes, you can put in bends in the venting, and yes it should be sloped.
I don't THINK 45 is necessary, just the usual slope so that rain or
whatever else gets in there can drain back down. And you have to be
careful that nothing drains in above the point where the vents come
together, of course, which isn't a problem in an attic. The rules are
likely different for the 3'' main vent than the smaller secondary
That said, our house venting runs all over creation, but we manage to
get away with just a single 3'' vent in the back, and a few of those
little under-sink venting things with the rubber flap.