Rough openings, headers, and integral posts
Cutting blank panels for rough openings slows down the wall assembly process. To minimize this factor, you can pay nearly any factory to pre-cut all rough openings for your windows and doors. A handful of manufacturers pre-cut their panels as standard; most charge a percentage fee or a fixed charge ($x.xx per square foot of wall panels).
Nailing off a header at a rough opening.
Typically, rough openings need to be cased with wood that fits between the panel facings and covers the foam. The wood provides a fire-stop material and gives you the nailer you need for attaching windows, doors and interior trim. Caulk the wood casing before attaching it. But before you do either, check the rough opening to see that it matches each window's required rough opening. If someone made a mistake, it's a lot easier to adjust the size before you attach the fitted nailers.
In most circumstances, rough openings less than four feet wide don't need headers; in these cases, the panel above the openings can carry the load. With spans wider than four feet, you will need a header to carry loads from above. Headers typically make up between 3% and 4.5% of the exterior wall surface area. To optimize the efficiency of your entire wall system, you should consider buying manufactured, insulated headers or building insulated headers on site. Headers will need cripple studs recessed into either side of the rough opening. Note that you will often have to patch over the header locations with either foam sheathing or OSB both inside and out, in order to match wall thickness for your finished exterior and interior; going with 1/2" insulating sheathing increases overall R-value.
Why not insulate your headers?
A few manufacturers offer a built-in continuous double microlam that serves as both top plate and header. The upside is that you don't have to spend as much time with rough openings wider than four feet, but the downside is that you lose some insulating value.
Where a beam is used to carry floor systems or roof panels, the beam is nearly always integrated within the panel. A panel joint should be centered where the beam must be placed. Then foam is recessed into either side of the panel joint far enough to fit half of the post-typically 2 1/4" to 3 inches (for either three or four 2x studs). In essence, the post becomes a "thick spline."