adding vinegar is simply a waste of vinegar- unless you need to (freshen) your water---
vinegar only sets acid dyes---
acid dyes are only used on wools and silks
so don't bother with the vinegar.
i pre-wash like colors together--reds together/ blues-greens together=== all (lights) together-
i use my regular detergent and warm water- toss in a color catcher if i think something might run/bleed
no fabric softener (if you plan to use any fusable product or marking product fabric softener can effect how it works)
i toss my fabrics into a hot dryer- i want most of the shrinkage to be done- i want any color running done-
then i lovingly iron my fabrics with starch before cutting.