Is there a recommended method of maintaining multiple Photos libraries on same hard drive My main Master Photos Library is over 400GB, and getting too big to tote around on trips.  I keep it on removable HD.  So I started creating new library for each trip.  Problem now is managing them all, and creating a master.  I use Power Photos (from Fat Cat) to move photos between libraries, but they don't support Live Photos.  A given trip might be as many as 4000 photos.  Some from SLR some from iPhone (Live Photo) and I combine them in the library.  Any suggestions on managing these and combining the libraries?
Honestly Photos.app is not really designed as a pro or semi-pro photo managing application. It certainly seems to handle larger libraries better than iPhoto ever did but if you are taking that many pictures and want to manage them on your Mac you might want to consider an app designed specifically for the workflow and archiving of thousands of pictures.

Adobe has an app for that (Lightroom, I think it is called), and like many Adobe apps is the subject of much praise and anger online. Me, I just use photos.app because my needs are met with photos.app, but it sounds like you might be better served with something more capable than a consumer level photo managing app. IMHO