How involved should an NCO or Officer get when Soldiers are making big life changing decisions?

I would say as long as the solder is receptive to receiving the advise, continue on or refer as necessary (don't overstep your own knowledge base). Beyond that, there is no way you can force advise on anyone. Just let them know you're willing to help as much as necessary or to get them to the proper source if it's outside of your level of knowledge.

Honestly as a PV2 I believe that the SGTs or COs should help as much as the soldier wants or needs the help, my SGT has helped myself and other soldiers with numberous things like getting our families here to Fort Riley, helping us make sound decisions on large financial decisions, and in my case helping me find a marriage counselor for my wife and I so In my opininon the CO or SGTs involved could help as much as the idividual needing it wants or needs in some cases

I believe you have to separate your professional position and advice from your personal position and advice. I have on rare occasion, expressed my concerns about a specific marriage or other major personal life changing decision to a colleague. But, this was never in any official capacity.