Split your task into 2 separate, tackle with single problem at once, not both together.
First get mouse to work and get your click results:
Whole documentation how to enable mouse interface:
When it works you need to use node “get hit result under cursor”. Then you break result blue node, and check what actor type you clicked on. Hint: you can also check what physical material you clicked, this can be used to “mark” actors that should respond to clicking (if you do not want to create separate blueprints for those actors).
Second part is playing matinee:
Creating matinee tutorial:
I think you can play matinee only from player pawn/controller (not quite sure here). So make matinee and then function to play it that you can call later.
When you can play matinee, it is time to make it all work together.
Easiest way is when you detect clicking in player controller (or pawn). Then You either check actor class or use that physical material trick. When actor class (or phys material) matches you play matinee.
Also you want to do UMG button, so watch this UMG tutorial: https://www.youtube.com/watch?v=yua1KSjJDdY
But first make everything working without UMG.