10g sure it would work... but 2 20s would look nicer... In your place to make this work and look good you would still need room to hide the canister in... my tank is right next to a cabinet so thats NBD If you couldnt do that then one large HOB on the back of the lower tank would work fine.
An over flow is simply a spot for water to come out of the tank by gravity.
The 2 main types are a hole in the back of the tank upper corner.
or drilled right up from the bottom.
Most folks at home do the back because there is room to do it Stores often do it through the bottom... I assume that is to save room from putting 90degree joints in the back.
Most people use a box this box has slits in it and fills up then the water goes from there down the drain to the sump or lower tank or refugum. ALL ... ok.. almost all SW tanks use this method.
Advantages..
- great o2 mixing
- pulls off surface slime
- lets one expand!!!!
- makes gravity work for you for a change
- lets you put equipment out of the way
- lets you increase total volume and footspace and still showcase in upper tank
Disadvantage
hard to make not noisy
If you don't really wish to have the tanks connected I would still get the double tank stand. As you said you wont have room to grow..
But you should have a minimum of 2 tanks.. everyone needs a your grounded bad cichlid or poor sick cichlid tank for those hard times
Anyhow this is what I would do
Certianly there is nothing wrong with a 20L - wood stand, can under the stand, heater, light, thermometer and food
