I can highly recommend the Salifert test kits. They are easy and quick to perform and simple to get the results and understand them.
I would recommend testing for the following parameters:
pH
Alkalinity (KH)
Calcium
Magnesium
Phosphate
Nitrite
Nitrate
It think these are the essentials to understanding the chemistry of your reef aquarium and being able to properly dose/maintain desired levels.
Much luck!
