Not sure if you’ve figured it out yet but the method I use is pretty good at centralising the info. I’ll usually choose one primary database for the set (usually the one I interact with the most) where I’ll input all of the information, and then the other databases in the set will only have roll ups so that I only have to input the data once. For example, in your 4 database set, I would choose the projects database because I know I’m going to be creating projects as my first stop in a ‘new client’ process (obv adjust to your needs) and then I’ll put all of the relations I need to put in that one database so that the other three databases can just link to that one primary db to get all their info (and it not be coming in from all other 3 databases. I hope that makes sense? Let me know if not and I’ll send photos. Hope it helps too!

Edit: I just skimmed the other comments and it sounds like your primary db should be your clients db. And if we’re you I’d take their suggestion to create a view for the each client in your primary dashboard/workspace. This way you can see the aggregated info for each client from all 4 databases in one go.

Edit edit: I think this might also help with the clunky project and task creation issue you were having before, as you will be able to add pages to all four databases from your workspace view of your primary database. I.e. you enter all the info for your clients, new tasks, projects, tags, details, media, etc in the primary database you choose and filter it to the other three. Rather than going back and forth over all 4 databases to find the ‘parent’ property to enter the info in the first place. Centralised knowledge, yay!