Going off of the manufacturer's recommendation of 10mg/hr per 25 gallons, I would recommend a 50 mg/hr ozonizer. I know there is temptation to go with a 100 mg/hr, but I would be careful. Most of the ozonizers have an adjustable output so you will have some control.
Definitely consider an OPR monitor and a HACH DPD Chlorine Test Kit for managing the unit. There was a post today in Reef Discussion "3 ozone questions." You might want to check that out for more info on using the Chlorine Test Kit from HACH.
Also, how do you intend to mix the ozone with your water?
Jim