Since I just talked to you, I would def. recommend phosphate and nitrate. If you want ammonia and nitrite, go for it, but you'll probably be testing those very infrequently due to the established time of your tank.
I think a lot of times we make the mistake of assuming that everyone on here is doing SPS/LPS, but in this case, the OP is not doing those for now. Until he does, having calcium, alk, and mag really won't be important at all. Before you do go sps, def. go get those test kits. Until you do, save the money and your time.