The YMOYL calculations are helpful, but I'm finding they do miss something that is somewhat unique to my current situation. In one day, I can do 6 classes (4 public, 2 part-time), which turns a nice profit for the day (~$175) for less than 6 hours of class-time. However, my actual "work day" would be from 10:00AM to 9:00PM in some cases. There are these large downtimes working here, like the 2.5 hour lunch time and the time between school gets out and part-time starts. It makes the day somewhat of an endurance race!
Private tutoring in the home would be awesome. It is one of many grey areas here, though, which also adds towards my trepidation to starting that hustle.
@Fish Thanks for contributing, I appreciate the different viewpoint. I'll be thinking about your words for the next few days I'm sure! My initial reaction was a bit dismissive, but that's simply a downside of my personality type, because there's definitely a ring of wisdom in what you say. I think my initial reaction stemmed more from perceiving "creatively unemployed" as having a negative sting to it

Scaling vs. not scaling... I can't handle scaling up my work too much right now since, as I mentioned above, the long "word days" require some recovery. I would only really want to add more classes in a row on a particular work day, or develop my own student base for private tutoring. Scaling up directly pushes ahead my ERE date, however. Right now, I'm assuming I won't work in the winter nor the summer, which sort of fits scaling back and enjoying my leisure time that you mentioned. Adding these three months of work into my plans knocks more than a year off my time in the rat-race.
Scaling back at this point, however, would directly pushed back my ERE-date, at least initially. I think the trade-off would be that I could develop/learn some sort of employable skill to use in a potential future, short-lived career. First thing of course to mention, is that I want nothing less than a career. I have a personal revulsion to it, which I can clearly explain how this feeling developed but it would probably bore you all. If I were to seek some career down the road, it would have to increase my annual savings to be the right choice now. This is a lot of hypotheticals, but one thing to consider is that in order to save as much as I plan to with 9 months of work here in China, I would need the equivalent of 12 months, 40 hours/week (at least), with a salary of at least $42,000 in the US. Since I would be scaling back in the present, in order to stay on pace my salary would actually have to be a bit higher, since I would have to make up for savings lost in the present.
I am working on some things, though. I'll be buying climbing wall materials and tools in the next week, which means I'll be able to pick-up routesetting/climbing gym part-times in the future (if I want to and they' exist where I am). I'm working on my game, which, if it sells, I'll be able to make extra money doing something which is super fun for me. I guess I could use that experience to go work for a game studio too, but that's a full-time job making something for someone else, which also repulses me pretty strongly. If you have some suggestions for skills to develop, that may be helpful. I fear most wise suggestions won't be suitable for me, though. I'm so picky. Plus, teaching in the US fits the annual salary I mentioned above, so that's always an option.
I don't want to sell something for someone else, I don't want to make something for someone else, I don't want to help someone with something... I think creating something of my own is the only sort of labor that I actually find tolerable. This pickiness makes it difficult for me to embrace losing income now in order to develop a (potentially) more marketable skill for the future, since most of the marketable skills are things I wouldn't do. This pickiness aside, even if I were to "suck it up" so to speak (not that I feel anyway is obligated to do so), I don't really believe that there's an actual marketable enough skill that I could develop now which would make the tradeoff worthwhile. I'd be happy to entertain ideas on what that skill would be though!