I’m not quite sure what you’re trying to do here. Are you

1. Trying to create a new owncloud instance and put your data somewhere other than in /var, or
2. Try to move the data location of an existing owncloud instance?

If you’re trying to do the second one, there’s a useful guide on it here: https://omiid.me/notebook/25/move-docker-volume-to-bind-mount. The first one should be even simpler, you can just replace the volumes in the compose file by bind mounts (basically, just this step of the tutorial: https://omiid.me/notebook/25/move-docker-volume-to-bind-mount#modifying-docker-compose).

The Windows filesystem: https://en.wikipedia.org/wiki/NTFS. Basically, don’t try to share the game drive with Windows.

If you have an AMD GPU (except for the very latest GPUs), you should be good out of the box. The AMD driver comes pre-installed with mesa.

Other than that… don’t use NTFS to store your games.

Edit: Maybe I misunderstood your question. I understood it as: What are some recommended changes to do after installing a Linux distro. Did you meant to ask about differences between distros?

AFAIK, this corresponds to the snap package of Steam.

What are the specs of your new computer? Mint can struggle with brand-new hardware (e.g. new GPUs from AMD/Intel). Or did you purchase a new PC that officially supports Linux (Mint)?