Hello, Marcus
I am not part of the GrowthBook team, but hopefully I can help you.
Regarding your first question, there might be a better option, but we decided to go with tags, to know which team has ownership over which feature.
Finally, regarding the experiments cross-technologies, you should be able to do this without any issue if the user attributes that are used to handle that experiment are the same. So, if you use userId to split the users, and you assign the same userId to that user, you will receive the same assignment.