Hi, you gonna hear alot from the 'experts'. Sometimes, the advice are just one's preference not necessary the ultimate must do.
My few months into marine tank teach me to observe and read more of what others have to say.
Not everything is a must but certain things are good to have. If you have a basic system, it does work just that you need to spend a bit more time maintaining the tank.
Yours is a 2 ft tank, if you keep it simple, you don't need all the skimmer, wave pump, sump, etc. Of course if you want to have big fishes, coral, anemone, etc, you need more equipment to sustain the environment.