Welcome to the hobby!
Similar to you, i also started off this marine hobby with a fluval 12g. Seeing as how your system is still new, remember to run through some test kits(ammonia, nitrite, nitrate) before adding your lifestock! Most definitely invest in a magnet cleaner, it would be extremely beneficial!
As for livestock, you can look towards a pair of clownfish(designer or normal) and perhaps gobies or smaller kinds of fish(fire goby etc). I assume that you do not have a chiller currently, so you should look towards gsp(green star polyps) and zoas as they are more tolerant of higher temperature than most corals. For inverts, you can look towards a clean up crew consisting of a variety of snails to help reduce waste and eat nuisance algae (turbo, nassarius, hermit crabs). I would recommend around 5 snails as a starter.
If you have any further questions, feel free to ask !