Andrew
For the long term health of your module and wall, please screw the standards to the wall studs - do not use the plastic expanding sockets in the wall board. As weight is put on the edge of the frame furthest from the wall, you have a 2 ft cantilever lever arm against the standard mounting point. Wall (gypsum) board that is not backed by wood at the mount point cannot sustain repeated loads like this without breaking down. If the plastic plug doesn't pull out eventually, the wall board will crack - more likely the further your mount point is away from a stud.
If you mount to studs only, your standard (track) spacing is going to be driven by the stud spacing - usually 16 or 24 inches, depending on construction practices and codes in your area when your house was built. 16 inch spacing is more common than 24 inch. The biggest problem is that stud spacing is often less than standard next to windows, doorways, and corners, making the look of the installation awkward.
I have heard several reports that the tips of the brackets did not line up in such a system. It may be the fit of the particular bracket in the track, or it may be your wall is uneven and the standards are not all in the same vertical plane. In either case, the wider the bracket, the more noticeable any variation will be. It might be worth carefully checking your wall with a level, and shimming (I use cedar tapered shingles cut to width with knife) before screwing the standards down tight. Differences in bracket tip height from bracket fit in track can be adjusted with some careful filing of the bracket.
Fred Wright