I would use RO unless its an elaborate planted tank and you are dosing ferts / minerals precisely.
As for supply, first off what ever your RO unit feeds into needs a float valve / shutoff. If not, you will forget its on and flood the room... multiple times. For big systems I used Brute trash cans and the wheel base, easy to drill for the float and move around to pump water into other things. I wouldnt suggest cheap trash cans or plastics as they can leech bad things, never had probs with the grey brute ones. For topping off your tank, I used an ATO controller with 2 mag switches and a small powerhead.
As for supply, first off what ever your RO unit feeds into needs a float valve / shutoff. If not, you will forget its on and flood the room... multiple times. For big systems I used Brute trash cans and the wheel base, easy to drill for the float and move around to pump water into other things. I wouldnt suggest cheap trash cans or plastics as they can leech bad things, never had probs with the grey brute ones. For topping off your tank, I used an ATO controller with 2 mag switches and a small powerhead.