If you’re going to do mostly fish, soft corals and Lps I wouldn’t worry to much about alkalinity and calcium. Usually it’s enough just to do regular water changes with a good salt mix for those mentioned.
Unless you pack the tank full of corals you should ok.
Now if you’re planning to continue to add corals and some sps then I would look into a calc reactor.
I never had a reactor and never got into SPS. I was always tinkering with diy things though.
Made up my own two part dosing with baking soda and calcium chloride solution for calcium and alk.
Tried Vodka dosing for Po4 removal.
Made my own kalkwasser mix for top off water out of pickling lime.