I agree with Ppowersteef. Completing Normal mode is a good idea.
However, Expert mode is very fun and frustrating at the same time. I, cannot play Normal Mode anymore because of how easy it is compared to Expert. Once you start playing Expert mode, you'll love it! There's a lot more things and challenges there, including great exclusive items and very fun boss fights (Good luck with the Wall of Flesh, by the way), especially if you have a friend who's down for anything.
If I were you, I'd pray and go straight to Expert Mode. Beating BoC in Expert Mode is no easy task however, so don't doubt your skills that much.
Have you completed Normal Mode, by the way? You'll have a better idea on Bosses since they are a pain in the behind during Expert Mode. Especially The Destroyer, Wall of Flesh and Plantera.