Been wondering the same thing and here's my take as I've begun to take course skiing more seriously this year.
I think you're on the right track with that list. We all struggle to manage life and skiing so the off water activities with skiing in mind (cross-training) are always a good thing. I've been focusing on three things to help my skiing - core strength, balance and endurance. All things that should help anyone's skiing.
As for the on-water time goes I would suggest starting the season with some sort of professional coaching. I've been skiing my entire life but wasn't introduced to the technical side of skiing until this summer and it was that "eureka moment" you referred to above.
A local club hosted a clinic with @CParrish43 and those 3 sets completely blew my mind. I had a break through morning and skied passes I barely touched my entire life. Fast forward a few weeks and those passes are more consistent for me and I'm pushing into more PB's as the summer progresses. I wasn't a bad skier before but the little bit of coaching has given me a lot to chew on this summer.
Once we got the season started on the right track I came up with a sort of plan for the summer. Nothing official or spoken and mine has varied week to week but I always try and keep my end of summer goals in mind. This has helped me stay focused on a few key aspects of my skiing and removed a lot of the "clutter" we all get caught up in as we try to progress. Of course, there's always that morning when you say screw it...lets go fast or cut the line to break up the routine....I mean we all ski to have fun, right?
Lastly, I would say finding people who can push you and refresh your memory on the coaching you had in the spring is a huge plus. I don't think it's fair to expect ski partners to become your coach but if they can help you focus on those core training tips from your coaching then you'll be able to keep it fresh all summer.