Yes. For the new database migrations to work, you first need to upgrade to 9.1.2, run sentry upgrade and then continue onward to Sentry 10+ (or 20.6.0).
Unfortunately there’s still no official guide for upgrading from Sentry 9 to 10, or for migrating from a non-Docker installation to our Docker-based installation. We are planning to have this in the coming months though.
Also, v20.6.0 is GA. It was tagged yesterday but we were already telling people to use :latest for everything. What this version provides you is a single version across all projects you can refer to, instead of separate SHAs, that are known to work well together. This should help you deploy Sentry yourself on AWS etc.
Sentry itself needs Python 2.7 still (work ongoing for Py3 migration) whereas Snuba uses Python 3.7. When using Docker images, this should be irrelevant as they are all isolated.
Those are all independent services, just using the same main application but with different parameters so I think yes (I don’t know what you are referring to as independent pods).