No. Some old-school plumbers and pipefitters believe that unions should be installed in one specific direction, and some apprentice training books even say so, but this is only a bit of folklore that...
Depending if you are talking about stainless steel or galvanised steel. Either way, you need to use copper compression fittings, otherwise known as conex fittings in some countries.
What does the schedule have to do with the material as schedule is the wall thickness Schedule 10, 20, 40 80 and 120 (XXH)
The Schedule is telling you the wall (INTERNAL) thickness 10, 20 40, 80...