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As I said you'll want to stock the tank lightly if you aren't adding extra filtration. You have a fairly poor quality filter there.
I'd reco you do 6 on the panda cories. IME they really start shoaling nicely once you have 6. BN's can be territorial towards eachother. I would reco you add them at the same time. Two BN's shouldn't be needed to keep control of algae in a 29, but if you just like them and want two that's fine. Just supplement them with a high quality algae wafer, blanched veggies like zucchini, and definitely keep some driftwood or mopani in the tank for them.
Are you still thinking about guppies like originally? A group of fancy male guppies would fit in there nicely.