Im in the same boat, therefore i don't use smf for community builder.
as far as i know, you have to use the SMF login which will sync to your CB.
Also, your "profile avatar" in SMF will be your CB avatar. Therefore you can't update your CB image to refelct in SMF. It needs to be updated in SMF to reflect in CB.
SMF doesnt allow you to replace it's profile system with CB, like Joomlaboard does.
I just really wish that Joomlaboard, being the only "true" forum for CB, had more support, developement and/or at least a road map.
If im wrong with any info, let me know.