Been trying a few things out in between "serious" campaigns. Tried out playing an ultra-loyal Byzantine vassal in 1066 Apulia/Longbardia in CK+. Let me tell ya, it's a hard life for the loyalist. Endless civil wars. I retain leadership of the Glory Faction in order to keep at least one of the factions in line, but I can't control the other ones. We're doing alright in terms of expansion: Georgia has been brought into the realm, as has Jerusalem, while I've expanded into South Italy. But the Imperial Decadence is killing us, and we repeatedly have to raise crown authority because the civil wars bring it down to nothing. I'm managing to expand fine: Norman power is declining; Spoleto is broken, and I had a great time when my friend the Basilissa immediately pushed my claim as soon as I had fabricated it; I'm in position to take the rest of Sicily (the duchy) soon. So the short term is ok, but the medium-term is concerning.
I'm particularly worried about viceroyalities, because I'm not 100% on how the AI uses them in CK2+ (which is the Imperial government type). I assume the AI will create the duchy titles as soon as they can, but what will that mean for me? Can I eventually create the Kingdom (or Exarchate I guess) of Sicily, or is that forbidden because it's subsumed by the Italia province? Thus far I've been careful to expand such that I don't get enough provinces to form a duchy, but that slows me down because it means I can't use dejure wars, and I'll need a higher tier-title eventually. It wouldn't be terrible for me to lose some of my titles, so for example I could Holy War for parts of Africa, create a strong little fiefdom, then peacefully relinquish it (as long as I have land nearby enough to Holy War); but I don't know if I can easily do so, whether it'll piss off my liege, or whether they'll decide to take away my holdings in Italy or some similar foolishness. I want to build a power base with which to support my liege (whomever they happen to be) in their wars and independently expand enough to form Rome. To do that, I want to have a free hand in South Italy for as long as possible and have some sort of stable realm with which to complement my liege.