First let me commend you on doing the right thing & looking for info first.
now there's good and bad about what you've got there.
-You can keep zoas, mushrooms, and many LPS
corals with the stock lighting of a nanocube in pretty much any location you want(this includes those "flowy corals" that youre looking for such as torch, hammer, & frogspawn on the sandbed) I know my frogspawn & hammer grew like crazy in my 12G nanocube under the stock PC
-the AIO system is an AWESOME tank for a beginner, you can get your feet wet for relatively low cost(in the SW
-You're going to want to upgrade the stock pump to a maxijet 1200 or equivalent
-You're going to want a powerhead in the tank. I recommend the korlia nano 425 for your size tank. It's small and has enough power for any coral you want except SPS
-Just in case you had the thought later, you will NEVER be able to have an anemone in there in general imo
. the tank is too small for a BTA or LTA long term even if you got brighter lighting down the road
-You're probably going to want more rock if you're looking to go reef instead of FOWLR
. general rule is 1-1.5lbs / gallon
changing the pump out is as easy as shutting the current one off & pulling it out of the plastic tube its attached to in the back. then just put the new one it. it should be just the right height so no cutting or anything is necessary.
Lemme know if you have any other questions. might want to start a build thread so people can ask all the other questions that come along with this.
Welcome & happy reefing