I'd tweak the physical damage resist of biters to make gun turrets with red ammo a feasible replacement for big biters. Uranium ammo or more guns with red ammo could work for behemoths.
I'd not use landmines, because they take an extra step to think from the player as you need to combine them with bots.
I'd not focus on laser turrets, because those may cause an accident where your base just goes down to power.
Gun turrets can also have resupply trains for ammo, so it may add some things to the Nauvis gameplay instead of taking away from it.