Bern helmets are awesome. I bought the watts this season and I already like it better than my smith maze. I am able a fit a thin hat under it with no problem, but remember that wearing a hat under a helmet can reduce the effectiveness of the helmet, especially if the hat is really bulky.
I have Smith Venue for the kids and me. Very warm no need for a hat. Most helmets are designed to NOT be worn with a hat. That is a whole other discussion. You can wear ear buds without any discomfort but a blue tooth would be nice. I prefer to not ride to music but that is just me.