Well, that’s a long story and you are also aware of PureRAW. 
I was wondering why you’d want to edit TIFF files in PhotoLab, skipping the noise reduction and lens corrections that should be done first. The latest version of PhotoLab now supports some AI features that can help with masking, but these are quite hardware-intensive. And while we have some layer techniques available, these are nowhere near as sophisticated as those in Photoshop …
Although I use PhotoLab together with FilmPack and ViewPoint, I still love and use Nik, as you have already mentioned, also together with old PS and Wacom tablet … , and use PS also for finishing prints.
With metadata, keywords, and the like I cannot help you (store my data as described here).
Test thoroughly, PL and the other components are not cheap.