Don’t know of a template feature in AE, but another way to do it would be to create a project, make any number of organizational adjustments, and save as ‘job_template.ae’ or whatever.
Each new job, open this file and ‘save as’ to another location.
Yeah, that’s the tricky part. I guess the first thing I’d try would be playing with the standard AE lensflares, paying attention to the kind of global light ramp that would occur when a ‘supernova’ was present. As for centering it in a 3D comp and having that be believeable, probably more specific to your particular file. Good luck!
Trapcode shine and Sapphire’s lighting suite are a pretty good start for this kind of thing. Some of the Sapphire lens flares can be used to this effect by centering, adjusting (or turning off) the pivot (secondary rings)