what do you guys do or have done? 

We are getting close to sheetrock for a shades project and we need to have the backing put up. My thought is to cover about 12" out from the wall (surface/outside mount shades, most ceiling mount). This should be enough for two shades, if they chose to do blackouts. Most windows are 7'wide by 10' tall and so double roll brackets won't work. 

we will be enlosing all shades with facia and covers. Any tips on where to bring the wire out?

From my experience, majority of the time your shades are going to be mounted to the window trim or the header. There should be more than enough without having to reinforce. Most shades are secured in 3 locations (both ends and centre) so the weight at each mounting point won't be more than 10-15lbs. With your windows at 7' wide your shades are probably going to mount in 4 locations, distributing your weight evenly throughout the frame.

In otherwords, you shouldn't need to provide/do any reinforcement unless there aren't any headers or the building is all steel

You're saying the windows are set back 12" from the wall surface with framing at the corner and around the windows, but only drywall between? You could use 1/4" plywood. The weight of the shades isn't enough to pull that down.