This is a great list, and it should be higher up in this thread. Most of it applies to longer-term investing as well (the area I work in).
1) I always tell this to people. So much of investing / trading comes down to your emotional reaction, and paper trading does not invoke these emotions.
Contrary to your #3, I actually suggest starting with a small amount they can afford to lose. Better to work out the kinks and/or find out you're not cut out for it before you bet serious money. It doesn't have the full psychological effect, but it can be a big wakeup call for people.
2) Absolutely. Grind it out. Every day you try to get a little smarter and make better decisions. Learn to love the process and don't lie to yourself. I like to rub my nose in mistakes to make sure I don't repeat them, but I also take a moment to appreciate things I did well, like getting out of a situation when I realize I don't have a handle on it, even if it means taking a loss.
4) No textbooks can prepare you for the mental anguish of watching your portfolio sink. You feel like the biggest idiot in the world, even moreso if you are underperforming the market. Of course, when you're up, you feel like a genius. Its during those times I find it wise to reflect on the not-so-good months to remind myself that I'm not invincible.
5) As Buffett says about leverage, "If you're smart, you don't need it, and if you're dumb, you got no business using it."
To add my own:
6) If you don't know what your edge is, you probably don't have one. What advantage do you have over the other market participants?
7) "If you want a good gambling life, make positive expectation bets." - Ed Thorpe, in Mathematics of Gambling