You will need a rough opening of 61" wide for a wood jamb. This will allow room for 3/4" material and shim space for critical shimming to get it dead straight and plumb. Will need more info for the R.O. height....
When you set your steel track to the floor, cut it so the ends meet the rough opening dimensions. Set the steel studs back 1 1/2" from the ends at the rough opening. A double 2X6 header with a plywood filler should work for practically any door of any weight you choose to use.
Screw the wood jack studs to the steel studs using coarse thread screws Same with the bottom of the jack studs where it sets in the bottom track. Set your header on top of the jacks and screw them in place. Ideally to the jack studs too, but you may need pilot holes to minimize splitting.
Be certain you use the proper set back for the finishes whether you are using wood jambs and casing or going with a simple drywall wrap.
I don't know how much room your particular bypass hardware takes up, but if you have your doors already and they are 6'8" and your track and roller use another 2" to 2 1/2", you have room for a plate under the joist. Secure it well to the joist that is over it, shimming it flat and level if needed and set the track directly to that. Use 9/16" thick wood trim to cover the track so it flushes up with the drywall once that is installed, then the trim/casing will cover the joint between the head covering and drywall.
The metal studs will be 1/8" wider than the wood plate. Using 9/16" material at the top should allow the 1/2" drywall and wood trim filler to lay flush with one another.