MrsDeVere, I specialise in solutions, not problems. So perhaps we can help.
"Unfortunately this delicate balance is due to be royally fucked up soon and I have no idea what I am going to do about it." That implies you are may be about to be made redundant? Set backs can sometimes be turned round into advantages.
"Should have worked harder, been born into a different family, not lost a child, not adopted a disabled child, not married a man who became disabled, should have become that rock star and by now I would have diversified into Llama farming or something...."
A lot of those things are not in your control although hard work is. Most teenagers and young people do not work too hard and they don't do very well which is why most parents hope their children will work hard at school and beyond. We cannot help our families. You presumably thought adopting a disabled child was a good idea rather than IVF or one from abroad so remember the good reasons that the disabled child was the right decision for you.
What else - man becoming disabled. Well you have a men,. Plenty of single full time working mothers don't or are paying to support one they used to have. Short of doing a health check before marriage that is a haard one to avoid. I suppose most of us do due diligence - has he always had chronic schizophrenia or depression so hardly ever works, is he 30 stone, can he instead run marathons with me are his family all well. However even with those checks still any of us could be disabled tomorrow, but it certainly cannot be easy.
I know people with Llamas. They are lovely cute animals but not much of a cash cow. Some women in later life manage to make it as a singer although it's rare - Susan Boyle etc. I sing every week if not every day and put probably about 10,000 hours of practice into it as a teenager so I am fairly good although I've never sought to make a living from it. If you are good start putting some stuff up on youtube of you singing, look at how the younger people generate an audience these days without financial backing if that's what you would really like to do.