@NIKOCRAFT - My understanding of Apache is that any change from the licenced file needs documented
every licensed file changed, a notification must be added stating that changes have been made to that file.
If a NOTICE text file is included as part of the distribution of the original work, then derivative works must include a readable copy of these notices within a NOTICE text file distributed as part of the derivative works, within the source form or documentation, or within a display generated by the derivative works (wherever such third-party notices normally appear).
For gplv3 and mpl seem pretty similar (from my layman's perspective). You really need to review each licence and translate to what you are happy for you software to be used.
Again as stated by myself, martinbean and danieloplata, having a licence file wont stop other developers cloning your repository (I'm assuming your going to make available via github or similar) and using it however they want from a technical perspective. What the licence gives you is recourse if someone does something that breaches the provided licence but is not an easy thing to pursue, either from a time or financial perspective.
I would think out some scenarios, both good and bad, over how users/developers can use your software once you open source it and how you would handle them. E.g. someone clones you repo, changes some basic css and repackaged as their own. Is this ok, if not what you going to do? Sue them? What If someone finds one of your vue components useful and copies it as is into their own separate project. Is this ok.
You have already spent the 2 years developing the product you can't get the time/resource back so I would focus on making your CMS the best CMS you can, adding new features, fixing bugs and generally fostering a community around the product, which shouldnt be an issue given your feedback to date rather than the little details of which licence to use.