I use Vienna Ensemble Pro to host the libraries and organize busses since I don’t trust the stability of a large template inside Cubase. For the most part, I bus by instrument type and articulation length, then section position. Primarily, my rule of thumb is to group by position / distance, but note length has to come before that if I want more control or need to add some instrument-specific EQ before the reverb.
Example instrument type and articulation via:
French Horn Ensemble (2 players) div A long
French Horn Ensemble (2 players) div A short
French Horn Ensemble (2 players) div B long
French Horn Ensemble (2 players) div B short
Trombone Ensemble (3 players) long
Trombone Ensemble (3 players) short
etc.
Each one of those has a send to a specific reverb + spatial plug-in strip set up for that section’s position. E.G.: Horns A and B would have their own specific send, Trombones and the low brass area have their own send, and Trumpets their own, too. Separating the longs and shorts lets me send them to their verbs in different amounts, since shorter articulations can get washed out a bit when used for repetitions. That’s just a thing I watch for now, but it’s not always necessary; I used get by just fine not doing it that way.
I send all those individual channels to Cubase’s mixer and group them up by section position. A “wall of brass” might be divided into groups like this: Trumpets (center), French Horns (left), Trombones & Low Brass (incl. Tuba / Cimbasso, right).
A really good course on mixing orchestral stuff and setting up a template can be found here:
http://www.alexanderpublishing.com/Products/Visual-Orchestration-2--Articulations-and-Templates__Spec-VizOrch-02-Dwnld.aspx
Grab it while it’s cheap!