Your question started off with testing water quality then into controller such as ACIII.
Basic test kits that you need to have on hand:
1. Ammonia test kit
2. Nitrite test kit
3. Nitrate test kit
4. pH test kit
Test kits that are necessary for salt water
1. Calcium test kit
2. Magnesium test kit
3. Alk test kit
I personally feel that a good controller is an investment in the hobby. Controller like the ACIII and Apex can monitor and help you maintain your tank's temp, monitor your tank's pH level, controls the lights, fans, etc. What it doesn't do is check your tank's ammonia, nitrite, nitrate, etc level.
The last thing that you need to have is an ATO (Auto Top Off). As your tank's water evaporate and it will, the ATO can keep your tank's water level constant, and thus less fluctuation in the salinity, etc. You can ofcourse not have an ATO but that would require you to manually refill your sump througout the day but that gets old and frustrating very quickly.