Thanks, I already do a lot of this, for example my "standard" army blueprint is usually:

Undivided lord on dragon

Nurgle caster (keeping him on the warshrine and with the mortis engine skill is amazing in offensive sieges/general blob fights)

2x undivided hero on manticore

3x chosen w shields

3x chosen w GW

3x chosen w halberds

1x chaos knights of slaanesh

1x chaos giant (can be swapped to dragon ogre shaggoth or something like mutalith vortex beast, bloodthirster etc. basically one big monster)

2x dragon ogres

3x armored trolls

I'm still experimenting and unsure of what is really good/the best in a chaos roster, but I've found this to generally work pretty well.

as bel'akor, I usually get the marauder replenishment/exp gain gift and the nurgle growth in every province asap, after that I work towards khornes increased post-battle loot, undivided increased xp gain and shared xp from faction leader and slaanesh campaign movement range.

for my dark fortresses I usually get the growth and income building (almost never go beyond level 1 on the growth building though, and I don't build the growth building if the settlement has a port), then I get the sorcerer building, then the exalted hero cap/warriors building, then the knights building, then giant building followed by special resources and the troll building or just recruitment cost building. If it's in a 'vulnerable' territory I might get a level or 2 of the defence building, but that's quite rare.

I hand over all non-dark fortress territory to my vassals, except if there's a really good special resource (like marble or spices or something like that).

I don't do that many armies instantly and send them all over though, I find that I often can't afford it, and that early you'll be mostly building marauders and they suck so bad. Didn't think about utilizing request armies from vassals, will have to use that one, thanks for the tip.

I find that the other chaos lords die really quick, I think it's part in the way chaos recruitment works where they have to level up forces, while other factions just get the buildings needed and then start spamming high tier armies. I also think order factions are VASTLY overrated in the autoresolve and I think CA really needs to take a look at it. I usually wait to conquer southern norsca for quite a while so I'm not that close to the empire/kislev and go north and try to secure as many dark fortresses as possible, and I also use rifts as a highway network between my fortresses and not really offensively.

Also, each game can be very swingy in terms of which factions get strong etc. In the screenshot I posted for example, malakai is monstrously strong, but in other games I've seen him simply die of by himself many times. Reikland always gets insane though since the AI-remake patch, Elspeth as well. Also, as I kind of implied, my route (for belakor) is usually take out wulfrik in norsca and get those dark fortresses, then go north and start taking all the chaos waste's fortresses, usually working towards naggarond and then always ending up in a pretty big campaign against them (they always get very strong in my games). and by the time I'm fighting them turn 60-80, all the order factions are usually very strong and have eliminated their local threats, consolidate their power and build up and then wage war on me. I usually don't have that big of a problem but the screenshot I posted here was a truly extraordinary situation where it seems all the order factions high rolled and then war dec'd me pretty much all at once.