Probably 95% of slabs poured with wire do not use chairs. While the wire is tougher to handle, get it laid down and tie wire it together, then while pouring, use a hand hook bent out of rod to pull it up into the concrete. Rebar on the other hand chairs are normally used, but old brick can be substituted.
Fiberglass is fine if you dont anticipate any heavy loads, though personally i'd never substitute it for wire or bar in a driveway. Let one trash truck do a turnaround and you'll have damage. At least with wire, should you have some cracks, (and concrete WILL crack) wire keeps it from splitting and heaving much better than fiber. Better to spend a little more now than have to have a section sawed out and replaced.
Another option would be blacktop. have you done a price comparson?
One last thing, for a quick material yardage calculation, sq.ft./80 will be close for a 4" slab. Dont forget to add 1/4 to 1/2 yard for any overages and miscalculation. Grade work is seldom precise so there will be some variation in actual mud poured.
Edited to add: Do Not drive on it for a week. it'll take that long to cure enough so damage isnt done.