Here's what I'd suggest, and the order I would suggest you get them to smooth out the learning curve.
Start with Ammonia, Nitrite and Nitrate from Salifert. You'll need these as you set up your tank to make sure the water quality is suitable. You should be fine for the first 2 or 3 months like that.
Next, get a refractometer with calibration fluid to make sure your salinity is accurate.
Calcium, Alkalinity and Magnesium will come next, but not until you start considering adding corals. For soft corals, weekly water changes will be fine to keep things more or less stable, and you can get comfortable with the testing.
When you start to consider stony corals, get yourself a low range phosphate from Hanna, and consider moving up from the liquid test kits to a Hanna for Alkalinity as well.