Reroll Shards

Hey guys, I have maybe 4 ancestral moduals i use for farming but they all have mythic level stats. I have around 277k reroll shards saved up and im using the cash Mastery to get more rerolls.

How should I go.about getting ancestral stats? How many stars should I save up to get all ancestral stats on a modual? Should I unlock all my mythic stats to try and get all ancestral stats or should I play it safe and unlock and reroll them one at a time?