Ninja hat + Viking Armor + Mana Staff with Temper, Heal, and Ice spinning around air-attacking makes your character practically invulnerable with heals and boosted attack/defense.
The hard achievement is much easier than the first rebuild's hard achievement because you can play a game on easy, level up 5 survivors in 10 of everything and then migrate them over to the new city once you draft a constitution or some of the other endings. It makes things muuuuuuuuuch easier on the harder modes.
If you want the badge, it's pretty easy like this: Max out the number of elevators you can have first, buy just machine guns and fill up your elevators evenly with them. When you can buy a laser turret, fill it in as the 3rd slot to an elevator (selling the machine gun if you have a 3rd one in the elevator). Keep buying elevator shafts and fill with 2 machine guns and 1 laser turret. Make sure the elevators with laser turrets are taking the hardest floors. Then start upgrading the laser turrets. You only need it to level 3 at the maximum and can probably get away with level 2 on every elevator. Make sure the elevators with the highest laser turret upgrade takes on the hardest floors.