I would just take the filter floss/one of the pads from one of your other filters and put it in the filter you're using along with some live plants.
The fish you're adding are a bit sensitive to new tanks, so you'll want it to be as stable as possible. The best way to do that will be to use your biomedia resource! (And again I suggest live plants.)
I like your stock list - have done very similar combos, though I never did the german blues, only the Bolivians - love the Bolivians as they are very interactive, as are the Angels. Not sure if you have more room but if you are looking for more fish to add once it's stabilized, some marbled hatchetfish would give you something at the surface that would fit your SA theme. (They also like an established tank.)