First thing first, what type of tank do you want? A reef, a fowlr
, or a fish only?
After this is decided, time to look at the basic hardline of it. First filtration.
For a 20g, you don't have to have a sump, a oversized aquaclear that is rinsed daily is great.
A skimmer is a either or here. If you do weekly water changes, you should be fine. If your looking at a longer time between water changes, a hob
skimmer would be a good investment.
A good quality heater is a must as well a high quality salt mix.
I use instant ocean reef crystals but standard on stand ocean is fine.
Api liquid test kits are a life line
A refractor or a hydrometer is needed.
Live sand, about a pound per gallon.
Rock, you can by dry an cure it. Save some money that way.
Of course a ph buffer if yours is not naturally around 8.0-8.3
Various odds an ins like 1/4 inch tubing, reef glue, spare mixing cups
As for stocking, two clowns will be fine in that size tank but I wouldn't add any more free swimming fish as they are damsels. I would add a shrimp an goby pair first then add the clowns. Maybe a type of cleaner shrimp an a few hermits