Most people inject it direct into a skimmer. Usually the ozone unit comes with an air dryer. You hook a small air pump up to the dryer then the dryer up to the ozone unit. Last the ozone unit goes into the skimmer air inlet. The dryer removes the humidity from the air (which gums up the ozonizer if not removed). I manually add Ozone at around 30-35mg/hr. You CAN hook up an ozonizer to an ORP controller but I'm personally not a fan.
1 - No, O3 (ozone) will degrade most silicone tubings. You'll need to find ozone-safe tube
2 - That's OK
As for where to inject it, do you have a model that requires a supplimental air pump, or one designed to run on suction?
Honestly, at 25mg/hr, I can't see how it's possible to OD a system that large... But if you want to control, does it have a scale or conversion to ORP (oxidative reduction potential)? or just millivolts?
Nah, calcium reactor is a very bad way to plumb in ozone.
I suppose if I were in your situation I'd start by trying the ozone on the skimmer and first see if there's even enough suction to pull air through the relatively small passageways in the air dryer and ozonizer. Adding all that stuff to the suction side of your skimmer may require you to use an exceptionally tiny air pump. I know in my own case, I had to buy the smallest air pump I could find cause the bubble rate went way down when I plugged in the skimmer.