I worked in commercial construction for 8 years and I've used a lot of metal track and stud.
It's been almost 35 years since I did it, but If I remember correctly, the sizes are: 1 5/8", 2 1/2", and 3 5/8".
I've used 3 5/8" track with wooden studs for speed and for getting very straight walls.
If you use metal studs, you should brace them against the outside wall by screwing a piece of plywood or OSB to the stud and the wall.
I would use pieces 1 foot long and wide enough to reach from the stud to the wall. This will stiffen the wall.
If you run electrical and/or plumbing, you'll need the bushings that fit in the stud cut-outs to prevent chafing.
1" screws to hang the sheetrock, and self-tappers to fasten the studs to the track.
Don't forget to make sure that the stud is square in the track, by putting a square on it before you screw it.
For those walls that you can get to both sides, screw both sides of the stud to the track to remove the flex and make it easier to screw the sheetrock.