Think hang on filter will do. Dun think u need air pump or skimmer. Just do more regular water changes. Basic test kits shuld include ammonia, nitrite (for cycling) ph, nitrate, phosphate.
U might want to get a fan or a nano chiller. Dun really need dosing pump as u will probably be keeping soft corals. Shuld get a ato instead cause salinity is going to be a main concern for a small tank. Or also can use dosing pump to top up water, but it seems such a waste.
For livestock ur choices are limited. Can possibly keep 1-3 nano size goby. And some shrimps n snails. Some ppl wouldn't recommend keeping fish at all. Corals u can try some hardy zoas or mushrooms.
This are all my opinion, I might be wrong. Maybe some other seniors can advise