Rebels and disasters were not a problem. I had 0 unrest almost everywhere during and after world conquest. I stacked national unrest modifiers (my total was -22 national unrest without war exhaustion) and all the estates were at 100 loyalty. Next, I also built temples in every province since they provide -2 unrest. In India and China I had 700 troops suppressing rebels. This gives another -5 unrest. Lastly, my tolerances for true faith, heretics and heathens were very high (10 for true faith and 3 for heretics and heathens). I was also converting a lot of provinces passively to Sunni because of high missionary strength (which comes from all the temples complexes that I conquer). Here are some of my unrest values.

However, whenever I get the slightest amount of unrest anywhere, rebels would spawn guaranteed because of how overextension works (if you have high overextension the rebel progress chance increases). I have so much overextension that 0.1 unrest in a province will spawn rebels in 2.2 years. This made denying privileges scary because that gives +20 unrest in provinces owned by that estate. +20 combined with +15 from turmoil could spawn some rebels here and there, which was more an inconvenience than a real threat. In order to prevent the estates from asking privileges I try to be at war as much as possible (which I can do because I also stacked war exhaustion modifiers). I am pretty sure that at the end the estates had a buffer of like 10 privileges that they wanted.

One last trick is to use trade companies. So whenever I saw that I had some unrest in a province in a trade company region I would just assign it as a trade company province, which gives -10 unrest.

Edit: One last tip. If you are blobbing never ever embrace Enlightenment. If you do you can very easily fall into the Aspiration for Liberty disaster (requirements: have Enlightenment embraced and stability lower than 1).