And to add more to your plate, if you plan on having multiple fish, a QT tank is a must..... you can roll the dice putting fish in, but if you bring in ich or another disease, marine fish are a lot more expensive to lose than FW
..... you should QT your fish for at least a month prior to placement into your main tank. IMO
, a small tank like a 20 long with a small heater and basic HOB
filter is all you need, but another added expense to consider.
On another note, you mentioned using RO
water for your FW
tank.... are you blending it or using pure RO
membranes remove most of the buffers from the water, so using pure RO
can cause a pH crash.