Hi, I’ll try to answer these until there’s an official response;
Butcher can’t make use of Strength in Numbers directly as he’s not a follower; his Devastating Assault special rule just improves the options for followers he’s leading.
Taking a guess that this is a mis-print and they should have a Soul Charge value listed (especially as bonuses from spending additional soul charges are directly referenced).
Bandits can’t normally be taken in other Factions (though there are cards for Neutral Mercenaries using the same models) so, unless it’s a mistake (which I wouldn’t know myself), Deeja can currently only be taken in Bandits.
1 - Strength in Numbers as per the Bandits Faction card only effects Followers, so Butcher’s Devastating Assault can’t effect them as they are not a Follower and therefore, cannot be effected by the base rule.
2 - Staff of Fireballs should have Soul Charges (3). Given that Staff of Ice Spikes does not require Soul Charges, I don’t think that item is missing anything. Please correct me if I am missing something.
3 - Deeja is a Bandit only model. That Adventurer Fortune Hunters box is a bit of a faction grab bag - the Serena model can be used in both Clan Vokihar and Adventurers, with the Dragonborn being in both Clan Vokihar and Dawnguard (off the top of my head anyway, I’m not looking at the cards atm).