This is going to date me terribly, but the first thing I think of around "Steady" is "Bebop and Rocksteady", from the Ninja Turtles. I was so surprised to read that it was used in a religious sense, I did not expect that at all!
I like the Puritan vibe Steadfast has (once I get past the cartoon rhino bit). I guess being homeschooled, he won't have to worry about being teased for his name.