What is the best way to maintain a large empire (and ensure a smooth succession)?

Hello! Despite playing CK2 for hundreds of hours I've never really played as anything above a king of a small country before. Now that I'm playing my first game as a Byzantine Emperor I'm becoming increasingly paranoid about the looming succession when my first character dies.

I've had an amazing start includes vassalising huge swathes of the Balkans and Asia Minor - including Georgia, Bulgaria and parts of the newly formed Hungary - but I feel like my current Emperor is mainly keeping things stable due to his high prestige, long reign bonus and being generous with titles.

So my question is, how can I ensure a smooth transition to my next character? And following that, what is the most efficient way to run such a large empire? Should I form king level titles to make handling vassals easier or keep everyone relatively weak as dukes? Should I keep crown authority high or keep everyone happy but a bit unstable?

Any advice is appreciated!