Thinking of turning my 120 into salt

[AquaAlexCardinale]

I have a 120 gallon freshwater tank..... but should I start as a beginner with a 40 gallon or should I jump right into the 120?
I'm strongly considering converting my 120 gallon into a saltwater aquarium I mean I already have the tank, stand, lights, glass covers, heaters, and 2 filters. All I would need is sand, live rock, salt, and a power head for fish only with some live rock right? What would the total estimate be? Do I really need a bunch of live rock if I were to say do the 2 aqeuon 75-90 gallon filters and if I put on a cansiter?
Thinking 50 percent base rock 50 percent live rock and live sand.

stocking will be:
- pair of clownfish, maybe 3
- large growing watchman goby
-bi color or flame angel
- blue hippo tang or quite possibly a powder blue tang
- lawnmower blenny
-and inverts...... crabs, shrimp, and maybe a chocolate chip starfish. my aunt had 1 in her old 180 and it was awesome

 

[lmforbis]

Sand Live rock for sure. You will probably want different lights even for fish only.
I'd say at least 3 power heads. Jebao makes some nice wave makers (variable speed and wave programs) at reasonable prices. I use 2 of those and 2 additional 800 gph constant speed power heads in my 125.
You can do mostly reef saver rock and a couple of live rocks. It will seed the reef saver. The bacteria on the rock is more important than the canister filter in a saltwater system.