Create state tree tasks to do your all/most behaviors. This keeps your actor BP super clean and lets you debug in the state tree debugger. Try to keep only the actor specific functionality in the actor BP, like setup stuff. If you break your tasks down enough you can call the VFX/SFX from there if it makes sense for your actor/game, for my game I tend to call gameplay cues from the task that manage that stuff over the network.
I think you’re on the right path using STT for everything.
I create parent STT for each actor type, do my context setup in EnterState there along with any needed helper functions, then inherit from that STT to create all the tasks for the actor’s behaviors.