After finalling making past the second night and into the third night I can say:
upgrades are overrated. the game tells you to do upgrades but having more turrets jsut matters more as a turret can still only kill 1 enemy at a time (if it can one shot it, assuming).
I jsut had this setting:
left side: 2 level 2 towers
right side: 2 level 2 towers and further right 1 level 2+1 level 1 tower.
the enemystill made it inside, dtroying everything except the inner most towers.
sure, having them on level 2 by night 3 is important since in night 3 anything beneath cant one shot anymore.
but having like many turrets one after another is more important.
upgrades only seem to increase the shot damage, not how frequent a tower can shoot or anything else.
Also something that disappoints me:
Since the beginning it was my goal to make a clear path to the right hand side mine, to put turrets right behind it.
Cause you know during the night, the mining bots mve only inside the area between the left and right side turrets.
so me thinking: if the right most turrets were past the diamond mine, maybe the bots would even drill at night as long as the mine was "secured" by turrets on the other side.
Nope, they still stay close to the fabricator and dont do shiet.
so any try in expansion is kind of pointless and increasing the defense around the fabricator seems to be the main goal for the first few nights at least.
and if anyone is wondering:
after having lost everything excpet 2 turrets and therefor basically having lost anyways, I went as far left as i could.
Sadly no spawn gate or anything, jsut after a while the trees and background and stuff stopped, only the water and the ground tiles still going.
so yeah, not much to find there yet. :-)
will keep grinding but given that it took me some min maxing and like 8 tries to finally make it past night 2, the game might still need some tweeking here and there :-)