The Baalz Drop Doctrine

[Executor]

While I am a big fan of blitzkrieg wars and try to implement them whenever possible, it is a very slippery road to take.
These kinds of wars demand an enormous amount of resources if they are to work, of course time to organize and test everything out to perfection, diplomacy to secure your borders before entering a high risk war like this and most importantly like you said to gather intel, which, like you said is never gonna be accurate as you'll want it to be, as better players will most probably always have something in their arsenal that they are hiding and waiting for the right moment to unleash.

The most important thing IMO is to watch for the counter tactics the enemy will use. Test out if your thugs/raiders can survive GR's, manifestations, infernal disease, earth attacks, and watch that the war is efficient in a gem to gem ratio, you aren't exactly winning the war if you're loosing/wasting gems rapidly.

Also, I'm not too fond of pillaging provinces, as the best course in war is to take over enemy lands unharmed, but once you raze your enemies lands you can raise an undead army with carrion reanimation to bring down badly defended forts.
Poping domes all over the place is not always a good thing either as you can gateway in an army next to a cut off fort and the enemy won't be able to teleport any reinforcements in, so that's another thing to consider, it can also be a nice way to sneak capture the enemies capital. Leave it be for the first few turns and when he vacates it to recapture his lands you take a province next to it, gateway in troops, send more thugs, and move in for the kill if possible.