I'm really happy that Brian has done a solo project. I absolutely love The Gaslight Anthem, and I can't wait to hear a follow-up to American Slang. I just think Brian's talents are extended beyond Gaslight, so having a side project like The Horrible Crowes allows him to keep making different music. I'd be great if we had a Horrible Crowes record between Gaslight albums. I would love to see him or Gaslight also do a cover album at some point. I can't get enough music from these guys.
As for a single...I think this is the kind of album I'd like to hear as a whole. I may cave and listen to a single...but I think it would be best served an album.
No need for them to do a cover album considering there's a half a dozen fan-made one's floating around. This is an older one (I don't have most of these myself, just found the picture online):
Also, AP user CellarGhosts put together a really great compilation of Brian's solo songs/covers that I can't seem to find now. That's probably the only (if any) inclination to how this record will sound.