I would suggest that instead of getting another group of fish that you consider getting more of the schooling fish you already have. The bala will grow too big for a 70l, and you should have at least 5 because they are schooling fish. Also, your glowlight needs to be in a group of at least six, as do your neons.
If you get pandas, they are one of teh more delicate types of cories, in most people's experience. The water conditions are pretty much the same as most other tropical fish. I think they would be okay with 3 DL.