Pretty much what everyone else said. Ouija boards are tools, not toys, much in the same way Tarot cards are tools. I think that my early mistakes with the Ouija board (and other communications methods) taught me a lot, so I won't say "Don't touch them ever." But I think that if you want to get involved with that kind of thing, study up, read up, find skilled practitioners who can teach you.
The biggest thing, Debi already mentioned- You don't know who you're talking to. You don't know what's out there. You don't know when you get gibberish back if it actually means gibberish. What is gibberish to you might actually be an interpretation of something with intent. And you could be dealing with a spirit that it's just mischievous, or you could be dealing with something actually dangerous. Do not believe or trust any message received through any means of mediumship until you are confident in your skills and your understanding. Fizz's experience was somewhat unique in that he was encouraged to get involved with demonology, and that's a big ugly can of worms.
I have had very bad experiences with Ouija, and also some particularly wonderful ones, as well. But they can open the gateway to things that you do not want in your life.
Also, my guess with the message you first received of Don't was probably a guardian spirit, angel, or loved one of you or one of your friends trying to shut down the session before it started.
Good idea! I'll run the letters through a bunch of grids, see if I can find anything. Maybe a few languages too.
I might not go towards a Ouija board again, but this intrigues me.