Optimal tire size I would try in model 3 is 195/60R17 from new toyota prius.
In that size you can also get wheelcovers easily and use just steel wheels.
Inside wheel covers surely works. Bigger wheels you have more benefits you will get:
My estimation is 2% savings with these 155/70R19 wheels in audi a8 project car. One of the reasons to avoid huge wheels as the inside gap also increases.