Point one isnt that black and white. Characters give fear immunity to their mounts and units, mount to their riders. There is nothing in the rules about war machines to crew, but then I realized its monsters to handlers, so nvm that. It was a genuine question for both the cauldron of blood and skinks/kroxigors, though.
I would recommend changing the move of the machines to 3, to avoid some tricky situations from mixed move units. Currently the hellcannon is the only one that has mixed move, I cannot really imagine a death rocket speeding away as fast as an ogre

The cant charge vs. must charge is interesting, though.
Also clarifications for beast cowers and commandment of brass. What works, what doesnt? Although multi unit types suck, I would think of making all the machines count as war machines, except for the purpose of movement, charging and combat. The main reason for this, IMO, is the fact that deploying war machines individually is quite a boost to the tactical power of the list.