Not massively necessary in all honesty, but glad it's worked out for you. I tend to wash on a high temp setting and then air dry. A quick note that if you dry them in a drying machine it will affect their dust collecting properties as it negatively affects their static charge.
I've used it and its fine but a cupfull of white vinegar in the water works just as well and is a lot cheaper
According to the 'experts' on Detailing World, the important thing with microfibre cloths is to use a non-bio liquid detergent rather than powder (as the powdered stuff can leave a 'scratchy' residue) and you shouldn't use fabric softener (or detergent with built-in softener)
Blimey. Been lobbing mine in with the towels and undies for years. If I had an expensive car I might take a bit more care, but they still bring a £4500 car up very well.