9 – Need some directions and advice on starting a new generation of Drupal

I have a multi-questions on starting a new generation, so far I am using Drupal 7 and need to move forwarder to Drupal 8-9

I am currently running Drupal 7, multisite on Ubuntu on AWS, a normal multisite, manually instaled and working just fine.

In line with new and faster tools such as docker and Aegir, I believe it’s time to change.

My requirements are:

  1. Latest stable Drupal
  2. Work on AWS
  3. Multisite on the same computer (directly or multiple Dockers)
  4. Able to be protected by let’s encrypt SSL

So my questions are:

  1. Is Drupal 9 ready for production? Do the above mention tools support it? Do most modules and themes supports it?
  2. Should I use Aegir? Docker or both?
  3. Can I connect some of the sites to an external Database
  4. Can I connect some of the sites to external file storage such as AWS/S3

And if most answers will be positive (as I believe it will), I would like to get some recommendation on the best or most practical tools to use and if possible could I also be pointed to articles or youtube tutorials to get me started?

Thanks in advance and my apology on the multi questions.