Beer made from distilled water will not be very good. You need some minerals in the water. Filtered tap water is much more likely to make a decent beer.
Distilled and reverse osmosis are basically two methods to make the same thing.
You cannot predict the mash ph from the water ph. You need to know the grains used too. Dark grains lower the mash ph for the same water.
Get the ez water spreadsheet, and read the brew science section over at homebrewtalk.com.