The Benelli Nova and Supernova will shoot any factory 12g shotshell from 2 3/4" to 3 1/2". This includes slugs, buckshot, lead and steel. Benelli doesn't recommend shooting steel shot through the full choke though. Stick with the Mod or IC choke and you will be safe to fire anything.
As far as cleaning goes, I run a boresnake through it once or twice after hunting or going to the range, and wipe any dirt or water off the exterior. I find the matte finish on the Benelli barrel is very corrosion resistant, especially around sal####er, compared to other brands I have owned.
I don't think you need to worry about breaking in your Benelli, and I doubt you will ever wear it out.