Pace, there's certainly a large number of unanswered and puzzling questions around the whole scenario. Let's hope the NTSB can uncover the pieces of the puzzle.
The timing of the flight does seem to indicate a post-party event, and probably a flight plan with all of 20 seconds planning involved.
It's quite likely alcohol was involved as well, I guess autopsies will soon indicate whether that was the case.
The biggest puzzle is as you say - the man had enough skills and intelligence to build the aircraft from kit form (although I note the RV-10 is available as a "fast-build", thus minimising the owners build input) - so you would expect he knew enough to understand C of G calculations and load positioning.
One would imagine he would be aware of MTOW - but it does seem to be a regular problem, that even trained and licenced PPL holders are often oblivious to their precise MTOW, and feel that manufacturers figures can be "stretched".
As regards the law and claims against his estate and insurance company - all I can imagine is that the lawyers are going to have a field day - as they identify law after law having being broken, a lack of duty of care to pax, and probably a dozen other reasons to ensure that payouts run into the multi-millions.
