Holy smokes thats a tall tank, armatus will definitely thank you. Very nice pickup.
Instead of a niger which gets beyond monstrous, maybe an irwini catfish or two (aka armored driftwood haha). Not the most active but I like them a lot, very prehistoric looking when they get bigger.
Pics real small so hard to tell. But if your going with a bio tower setup plumb the overflow into a mechanical prefilter (multiple levels of mat, floss, socks etc) run three of the pumps pulling water from sump flowing directly back to tank and use the remaining one to pump water from the sump to flow water over the bio balls in the tower. Tons of ways to do it just depends on space and personal preference.