We wish to migrate Bitbucket, standard version, to on premise. If any one has done this please share your advice on possibility, pre-plans, risks involved, points to be considered etc.
While I have not done this personally, I can point out a few things you will want to consider when doing this move.
First, are you using BitBucket Pipelines? This don't exist in the server version of BitBucket, it is handled by another Atlassian application called Bamboo, while it should be able to handle the pipeline YAML files, this will be an additional application you will need to purchase and install before you can complete your migration process if automatic build are important to you.
This process will not metadata such as permissions, comments, pull requests etc. so this is information that you may end up losing as a part of this process.