Clear a wide perimeter around your area including mines, set up walls in narrow areas between water and send trains to supply them with bots/ammo/repair packs. Best defense on Nauvis is tesla turrets + gun turrets with uranium ammo, before that it's flamethrowers + gun turrets. Lasers sucks but can still be convenient for defending against light attacks in places where you don't want to send supplies to make a proper defense. Also put lv1 efficiency modules in all miners and build a nuclear plant, ideally with 1x2 or 2x2 reactors. Coal power has a hard time keeping up in late stage Nauvis and solar sucks.

>>717752730
IMO it really doesn't make sense to build more than a minimal yellow/purple setup just to have it and buffer up while you research other stuff until you can set up foundries on Nauvis.