Awesome! Dual stage regulator! Haha I have a nice AirGas dual stage regulator with swagelok fittings and needle valve. Wouldnt trade it for anything else AND it came out cheaper to build then the aquarium plants regulator that most people use.
As for the calcium reactor, I would only run one on a larger system. Youll run into clogging issues from a slow drip because its too much for a smaller system. A Geo calcium reactor is a well designed reactor and is about the same price of that Vertex one that's on sale.
And I personally think that calcium reactors are "nuke proof". Invest in a great solenoid and have your aquarium controller do the rest. You wont experience those end of tank dumps because of the dual stage regulator, which is the main reason why I decided to use one. My only concern would be your ph dropping in your tank but that is an easy fix by just adding a second or third chamber before the effluent hits your tank water. Calcium reactors, when set up right, should never have to be tinkered with. A true set and forget system. Plus it is cheaper in the long run and less of a hassle. Dosing pumps usually have to be re-calibrated every so often and that can be a pain. Hope this helped! Good luck!