So it 4x2x2, that a nice size tank to go on with.
TBH, a sump that is big enough to hold your skimmer (always going to better/cheaper than a HOB, as PuttPutt points out, and, second hand is always a winner) and gear would be ideal, your live rock will be mostly in your display (nothing wrong with that at all).
and you'll be over the 500L mark, making it very stable, both thermally and chemically.
I'm a slight jelous... Your going to end up with a VERY nice tank. :thup:
Don't let the idea of costs drag you away from it, Rome wasn't built in a day, and patience is ABSOLUTELY a virtue when it comes to marine, remembering that you probably wont be stocking out for at least 2 months, preferably 3... plenty of time to save up for different bits and bobs, and to do your research.
EDIT: oh, and you wont need to have a HUGE amount of lights. 2x 150w MH would do just fine, and if your not looking at polyps or corals you could get away with just flouros...