You're going to need more than one powerhead.
Do you have an accurate high-range thermometer, a reliable heater that can maintain a solid temperate of 76-80 degrees? You'll also need a reliable test kit. A lot of people get the API ones, but the Salifert ones are the best liquid kits (but pricey!).
You don't need to buy live sand. It's a waste of money and while it can help to get your cycle going, you're likely not going to need it if you're planning on 4 weeks. That's a good amount of time. Just buy regular aragonite sand and it will become live well before the 4 weeks.
Also, people here don't really like them, but I really like the liquid bacteria populations like Microbacter7 which you can buy. They contain all sorts of nitrifying bacteria and good stuff for the tank. Most people say they're not necessary, which they aren't, but I like the fact that they provide a large variety of types of bacteria. I figure, the more variety the better.
Protein Skimmer:
I highly recommend the AquaC Remora skimmer (with the maxijet 1200). I bought mine used (spent $40) and it's great after a good cleaning.
You don't need a skimmer though for awhile. Cycle the tank without one for sure and look into getting one when it's finished. :-)