My opinion and my personal experience.
Opinion - 125G is definitely too small for your stocking, even if it were a bare tank. But you are filling it with nice decor etc which makes it even smaller still. Regardless of over filtering, maintenance etc... I just don't think you have the space and volume. Sorry.
Experience - I had a 110G setup as a permanent home for 18 Colombian tetra, 6 silver dollars and 3 pictus catfish. It had a silver arowana in as a temporary occupant until it outgrew. I loved this tank so much! The aro left everything alone, if it wasn't at the surface it wasn't interested. The SDs left the aro alone. The Pictus occasionally had a Colombian tetra (I would lose about 1 per fortnight) but that was it.
I hope that helps?