Sacred Haven of Debauchery

When there are >5 planets, they will force you to introduce sectors, and the sectors will be self-governing.

It used to be five, but now it's more like 7-9. It depends on whether you play as a pacifist. It could even be 11 if you take the corresponding perk.

True, their self-governance isn't perfect; sometimes you have to temporarily remove individual planets from the sector and do something in them (improve the administration building, for example), but overall, the AI handles it.

The sector AI has improved after the patch, but it still sometimes does strange things. For example, it builds a regular power plant on a beta-rock.

I hope this game doesn't have rebellions.

It has rebellions. Sometimes, a planet can quietly break away from your control and join another empire if they have similar political views.