I did the same thing with my kids about using the real St. Nick to morph from believing in Santa Claus, to learning of the real St. Nick, to talking about him being a hero only because he lived his life doing the love God, love your fellow man thing. And I'm a Protestant -- I'm an example where we can use church heroes as examples even if I disagree with the Catholic church's canonization of saints (because I believe all believers are saints, not just a select few) and certainly disagree with praying to dead church heroes.
However, the tales of him striking Arius might be a bit far-fetched. We're not even sure he was at the Council of Nicaea, although if I had to put money on it I'd say he was. We do know he was against Arianism.
And don't make the mistake I did many years ago when I heard St. Nick was against Arianism (the believe that Jesus being incarnate undermines God's monotheism), which I mistakenly confused with Arminianism (the belief that we're not all pre-destined to be believers/non-believers).
Obviously those in Heaven are all saints but the Church sometimes canonizes people whose witness was in some way remarkable. They have canonized abused women, recovered alcoholics, pious parents, etc., in other words very ordinary people who cleaved to God through trials. This is done as an example to all of us that, no matter the circumstance, holiness is our goal.