If you are just planning soft corals (don't confuse LPS as soft corals, such as frogspawn...it is a hard coral) then you don't need to worry about dosing or using a calcium reactor. Especially when you first start up your tank the demand will be very low. You will be able to keep up just by doing water changes. Be sure to test your freshly mixed up (for 24 hours) saltwater for calcium, alkalinity, and magnesium and dose the newly mixed up saltwater if needed. No point in adding water to the tank that's low in one of the parameters, right? If you proceed like this, and do 10-15% water changes every week you will be able to keep the parameters stable for the first while.
Having said that, I would suggest dosing pumps instead of a calcium reactor. They take up a bit less space. I use the Drew's Dosers from
www.bulkreefsupply.com with digital timers I bought at the hardware store. I just use them for calcium and alkalinity, the magnesium stays steady with water changes. Calcium reactors use CO2 which will lower the pH in the tank a bit. Calcium reactors are also big, bulky, and ugly I think!
Dosers are way cooler looking, and they are easier to fine tune.