We're childfree, for some of the reasons you mentioned: lack of "burning" desire to parent, overpopulation concerns, spouse practically raised two children already (younger siblings).
1) We did become each other's best friend, and that makes a big difference. We've actually never had a "group" of friends (childfree or otherwise) until recently, and now the friendships we're developing are with mostly empty-nesters. I'll tell you what I believe we should do (not intending to presumptively include you in "we" [unless you'd like]): Our church begs older folks like us to volunteer to teach Sunday School. I think that would tend to expand our circle of friends to include parents. I doubt we'll do it though; at least not until we've retired.
2) The ACA includes the EHB requirement: The required categories for essential health benefits include: ambulatory patient services, emergency services, hospitalization, maternity and newborn care, mental health and substance use disorder services, prescription drugs, rehabilitative and habilitative services and devices, laboratory services, preventive and wellness services and chronic disease management and pediatric services. Including essential services in all policies within the pool helps support the affordability provisions of the law.
3) First, I never consider gifting a quid pro quo arrangement, so the fact that we had no bridal shower, our wedding was sixteen people jammed into my mother's living room ("no gifts please"), etc., and of course, no children, had no impact on what we give to others in those "gifting opportunities". Second, we give the lower of what's expected and what we can afford.
4) It wasn't easy. To be honest, right now I don't remember who we designated. It was between my older brother's wife and my spouse's cousin: The former is a very level-headed, responsible person with a strong medical background (relatively speaking - she was a insurance coder), but she lives 200 miles away. The latter lives just 40 miles away, and is a doggedly determined person, who will be a needle in the side of any hospital not giving us our due, if it comes to that. The key is that there was never any second thought about trusting either of these two people doing the right thing, vis a vis protecting us and our money, if need be.