I know this is old but in case anyone’s runs into this:
To answer your latest question, you could create a helper function to wrap "Get Game Mode > Cast to Sim_Mode > pull off Sim_Controller ", that way it becomes “GetSimController” and you can use it immediately.
That function could potentially be a member or even a global function as described here:
Of course what you mentioned about doing it in the BeginPlay could also work, but it could be nicer to avoid storing it everywhere and potentially having stale data (albeit unlikely).