Your algae is aptasia, (get rid of it) and you already have too many fish for a thirty gallon.
A sump is a tank under the display to hide the ugly stuff, nano means small, it is debatable on where to draw the line between small and nano. You can add plants whenever you want, most fish will eat them, depending on the plant.
You can get by with a simple canister on a small tank with fish only but with time your going to want more, and bigger.....
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