You may already know, but the smaller the water volume the quicker the water parameters can change. If you are on top of things and good about keeping all your levels (ammonia, nitrite, nitrate, ph
, alkalinity, phosphates, calcium) where they should be, then you can have as small a tank as you want. The bigger the water volume the more forgiving it is to changes in water quality.
As for the two fish and a cleanup crew, that is what I started with. I think its a great idea to start slow and get used to what you already have before adding the next cool fish or coral.
39 gallon (2yrs) 40lbs live sand. 23 lbs LR
(still collecting) , 1 turbo snail, 5 Nasarius snails, 10 blue knuckle hermits, 1 zebra hermit, 1 scarlet hermit, 5 red tip hermits, 1 Green Chromis, 1 Blue Damsel, ? Ricordia, candy cane coral.
135gallon (2 months)
125lbs live sand, 100lbs live rock, 2 175W Metal Halide, 1 175W VHO Actinic (so far). Berlin Protein Skimmer in 40 Gallon Sump. 2 Maxi Jet 1200's. 10 Nassarius, 10 mexican turbos, 10 astreas, 20 Blue Leg Hermits, 20 Scarlet Hermits, 5 Emerald crabs, 5 peppermint shrimp. 1 Copper Band butterfly, 2 False Perculas, 1 Javanese Damsel.