That tank is way too small for Archers. You need 100 gallons plus. Even bigger if you want to lower the water for them to shoot at prey. Loads of info about them on the brackish board. Do a search.
Go back to thinking Africans. West African biotope for you.
10 Congo Tetra, A pair of Yellow Cheek Kribs, 1 African Butterfly, and a pair of Upsidedown Catfish(sydo nigriventris). And if you can find a small grower get an elephant nose. It's pushing it but of everything else is happy and you find one, try it out.
After you cycle, start off with the Congos and some java moss. Expect to loose a couple. Pick up the butterfly and the upsidedown cats at Petco soon after.
Do a lot of reading up on the Kribs and test before you buy them a few weeks later. You'll be happy and so will all your fish. Especially when it's time to rip the legs off some crickets on "Live Food Friday"