The protected ones fit, but barely. They are a little longer so the cap doesn't screw on all the way. You can charge the 510 mega batt on a regular 510 charger.
I'm not a big carto fan, so I can't give an unbiased opinion.
Much more vapor with the HV units. Your throat hit will mostly depend on your nic content, but the HV units put out a warmer vapor which seems to help with the throat hit. The money you spend on the Joker AV will be money well spent.
I have noticed my VG flavors tend to be weaker than PG. I pretty much just vape PG now. There are suppliers like DYI Flavor Shack that sell doublers (extra flavoring) with their juices.
This is what I have for my SB; http://www.batteryjunction.com/4parc390reli.html
You don't have to use an 18650 with the SB. Altsmoke just states that in case someones stacked batteries blow up.