Yes, given that situation you will need to merge UI’s/blueprints etc. together for anything like a player controller where you can really only use one (at a time).
There’s nothing wrong with checking with the content authors and see if they will help facilitate that in the future, but don’t let it stop you. Don’t ever stop your project waiting for someone else to do the work for you! 
Good news is, copying-and-pasting between controllers and things can really help speed things up.
Hello. After much talk and no action I have started to get serious about becoming a UE4 games developer which is my dream and passion. I’m at the stage where I am setting everything up to begin making my game whilst learning C++/blueprints on the side.
However I am slightly bewildered on how to best implement assets that i’ve bought from the unreal marketplace into my game. I know how to migrate them now but I have another problem, for instance I recently bought a Inventory system and a stamina system and they both come with individual character controllers and UI HUDs and as far as I’m aware you can only specify one HUD class and Character controller in the world settings.
I guess my question is what is the best way to integrate these systems into my project? Should I be merging UI’s/blueprints together and stuff like that? I would appreciate if someone could point me in the right direction.
P.S If you are curious to what game I am making it’s an open world FPS Survival game.
Thank you.
I would have to disagree spawning actors to be used in such ways defeats the point of using a component, this is coming from some one that merge both of these system together in 30 minutes, the main problem is the stamina asset the developer should of used the component more, rather than just using it for his stamina logic, also the stamina system is made to be a template to build off.
components are good as well, especially for a stamina system, but for an inventory system, you might need gamepad input, which actors can do, but components cant. either way, moving code out of those common game framework subclasses event graphs, and refactoring it into custom components or custom actors, makes merging projects easier.