Welcome to the board & the obsession!
my 2 cents: Invest in a better skimmer, if HOB is the way you want to go that's fine, but take my word for it spend the $$$ on a good skimmer. Consider the Deltec H.O.T. Here's where having a sump becomes nice as it opens up a world of equipment possibilities.
FOWLR is an excellent way to enter this hobby, your flow should be good to start, the trick is what you do with it. Chaotic turbulence, or surge it with a wavemaker, just mix it up, even in a FO set up.
Buy a good variety of LR. It's okay to get a lower quality rock & the get a few "cherry" top -end peices as this will seed the tank nicely.
I would triple (at least) the ammount of sandbed myself, but I'm partial to deep sandbeds as part of my filtration approach. There are many ways of setting up an aquarium. Stick with easy math: "X" ammount of critters in my aquarium are producing "X" ammount of waste. What do I have in place to deal with it? i.e.: Skimmers, H2O changes, carbon & resins, UV, LR + LS, refugiums....blah, blah, blah.
Lastly use the best water you can find/steal/make, you will save yourself alot of grief.
Good luck. Rant over
