Are you trying to make a permanent tattoo, or just draw on yourself? If you're just drawing on yourself, fairly low unless you draw a LOT. There are inks you can buy that are specifically for drawing on skin.
If you are actually trying to do a permanent tattoo, first I'll tell you that there is a very high possibility you'll mess it up, get a big infection, an/or scar very badly. Then I'll tell you that pen ink is not designed to be in human skin, so it will probably break down and yes, poison you.
It's not a wise thing to do. You never know. The ink won't poison you unless you used a lot. The risk comes from infection due to the process. Add to that you'll have some ugly tats that will probably stay with you for a long time
Very very very unlikely. Your body flushes those things out but you might get a small irritation wherever you drew. If you were trying to make a real tattoo always use things like Indian Ink. It's the ink they use for real tattoos and is not harmful