I'd say that if you are going to invest money, dump most of your money in good lights (MH preferred) and an RO unit.
I myself like the PFO retro's with iwasaki bulbs, but that's a personal preference.
3rd thing I'd say is a skimmer.
And, if you want to save some bucks, try DIY.
DIY sumps, DIY skimmers, etc.
O, if the tank isn't filled, DRILL IT before you put water in it. Makes a world of a difference.
whirley