(( The Peacemaker,
A couple of quick thoughts about your proposal.
1) For the Hellstorm Rocket Battery, 3 Rockets is huge! When we tried D3+1, D6, or 3, the D3+1 gave the right "feel" to it. The D6 and flat-out-3 gave the Rocket Cart too much power during the shooting phase. Not to mention, you can get the Cart a bit more reliable with the Crew or Engineer reducing scatter by up to 4". And, smart selection of initial target-point, can basically nullify the effect of a 2", 4" or 6" scatter, as well (despite the potential 360 degree scatter arc.)
At D3+1 (2 - 4 rockets per turn). It was still unreliable in it's volley, but, for the 120 points, it at least was in the same price-range as a catapult... as we were equating the price of the Rocket Cart is reflected in the number of Rockets you get from it. If you get 3 Rockets, you're basically saying one Rocket is worth 40 points.
1-A) Something else we were playing with was the idea of "Walking" rockets. That is, after your first Rocket scatters, any other rocket templates can be placed next to the scatter of the first... which ends up giving a "walking" effect.
2) No love for the Empire General? You mention the Empire Captain, but don't give any new options or bonus' to the Empire General.
2-A) The most predominate suggestion I've seen, that's simple to apply, is just give the Empire General - Elector Count, the option of allowing one of your units a Magic Banner.
Anyway, just some input. I'll take a bigger look at it laters. ))