I would just take out the threadfins and then it would be an ok stock. Tetras it's preference you could do both and it would look good imo
Problem is i live in toronto canadaI'd recommend jeff rapps at tangledupincichlids.com over liveaquaria. Have heard stories of people getting incorrect fish from there.
Most small south americans would be ok to have a pair or harem of with a uaru in a 120, IMO. Maybe reduce tetra count a bit to make up for it. As rocksor noted, uaru are prone to HITH- so you've got to keep their water really clean. Easier to do with less fish. 2x water change a week at least would also be recommended.