1. correct..
2. grass will regrow if its outside your tribe area so yes.. but piles do not regen if you pull from the "actions" menu no matter if its in or outside your tribe area, thats how piles get wrecked.. always use you scavenge when possible..
3. no you have this back to front... grass will not regrow on terraformed ground no matter where it is..
4. again you got this back to front from #3...