Dolomite takes around 24 months to breakdown, depending on the total volume of soil, you may still have sufficient values. Your unlikely to venture into an elaborate testing kit for various elements, but a simple slurry sample tested with litmus paper can show the pH. Since I'm assuming your peat based, your pH will be low if your lime values are lacking.
As far as magnesium sulfate.... I wouldn't add it unless your adding lime. Plus it's always easier to add it in a foliar or drench if you do have a deficiency. It's easy to add, it's much harder to remove. You don't want to flush any formulation of supersoil. Less is more.
Alternatively you can contact your local county extension office for soil testing. Or private companies. Just have to mail a sufficient size sample and pay for the tests you wish to have done. Go with a NPK, Ca/Mg, pH, sodium and organic matter test.
