Also keep in mind that the rule of thumb as to the AMOUNT of fish you can have in any given tank is 1 inch of ADULT fish per gallon.
That is only with tetra-like fish (slim and long). That one inch per gallon rule should be thrown out of the window!

Jessica answered your othe questions perfectly, the only thing I would add is LIVE plants, they help your tank and fish out a lot.

Try to get a mated pair of dwarf gouramis, two males might have agression issues.