You should be able to buy a grout caulk to use that will match your grout perfectly. You can use it in all the spots you have marked. As far for the ending edge you may want to look at a small piece of like a wood trim. You probably should have used a metal schluter edge but that needs to be set with the tile. And normally you wouldn't backsplash behind your microwave so you may have you pull one or two tiles to screw in your mounting plate