Hey, welcome to saltwaterfish.com!!
Salifert is among one of the most accurate but most expensive on the market and Aquarium Pharmaceuticals is among one of the easiest to use and cheapest. I am not sure which route you were looking to take as far as test kit.
Proper water levels:
pH - 8.2
ammonia/nitrite - always 0
nitrate - under 20-30 for fish only, under 10-20 for a reef. Preferably, if possible, 0.
kH - 8-12 dkH, 143-214 ppm, 2.86 - 4.29 meq/l
calcium - 400-460 ppm
magnesium - 1200-1280
salinity 34-36 ppt (refractometer)
specific gravity - 1.025-1.026 (hydrometer)
temperature - 76-82 (stability is more important here)