I'd like to compliment you on the very innovative strategy. In this case, only repair droids can cut it easily, they don't even need guard droids to tank for them, because no enemy will manage to drop a single stack of those, and the other one will be able to repair the first one easily. Not to mention that you can even split them in even more stacks and compensate for the enemy numbers or attacks, even if most of the enemies inflict magic damage, to which the droids are most susceptible (even with some + magic def gear on).
As for the cool units, I'd add the Black Knights. Although their usefulness has been discussed plenty of times, having them kill an enemy and wait a bit till they start laughing at their slain enemies takes the cake in my opinion
