new....

Currently have an 55g undergravel that has been up since Nov 1.
Have 8 fish that I'm getting rid of at the store.....don't want the style.
I want to change to a rock / clown / pigmy angel tank is why.
Current filter is a MAGNUM. Change filter every week.

Tank located in a very visible spot in dining room.
I have plenty of power heads.
I have a protein skimmer that is not currently hooked up


Please help with:
--recommendation for filter that hangs on back.
--what kind of rock to get
--do i need sand? under my current UG I see quite a bit from underneath.

Thank you ALL for your assistance!!
Lof