I would do rock, then sand because of sand sifting fish and what not. This prevents them from digging under the rock and causing a tumble in the rocks lol.
as for the 30-40 gallon, i would go as big as you can. The bigger you get the more costly the initial setup will be but you will be happier with the look of it. Smaller tanks do require more work on your part and if you okay with that, then go for it. I would also consider getting the tank drilled so you can have a sump. Canisters on slat are not really the best idea. Sumps are the way to go. At worst get a hang on filter, that you can change the floss in easily enough.
as for the 30-40 gallon, i would go as big as you can. The bigger you get the more costly the initial setup will be but you will be happier with the look of it. Smaller tanks do require more work on your part and if you okay with that, then go for it. I would also consider getting the tank drilled so you can have a sump. Canisters on slat are not really the best idea. Sumps are the way to go. At worst get a hang on filter, that you can change the floss in easily enough.
