Although you have listed some useful resources, I completely disagree with you
I don't think the average Bitcoin user needs to know how Bitcoin works. All they need is a wallet, and start using it. There are some pitfalls, but modern wallets take care of most of them already.
Back to the example of your mom: give her a funded paper wallet, ask her to install a wallet on her phone, make sure the backup phrase is secured, and let her sweep the funds from the paper wallet into the phone wallet. After that, she can use Bitcoin!

Of course there's the generic "don't invest more than you're willing to lose" (Google gives 86 million hits so I'm not quoting a specific source here), but that goes for all investments.

You should try to explain the basics in a few sentences, like: "Bitcoin is electronic cash, you and only you are responsible for your own money, there is no undo-button, the value can go up 1000% or down 90% in just a couple of months, and scammers are always trying to get it from you so be vigilant".
I don't think this has to be difficult, because that would mean Bitcoin would never be able to reach mass adoption. And if you think Bitcoin is difficult, try explaining fiat money! I'm still flabbergasted when I think of a private organisation that prints our money out of thin air, which caused almost any human and any government to be in eternal debt. The fiat money system is much more difficult to understand than Bitcoin. Makes you wonder why they never explained that in school doesn't it?