You can go as low as the ground effects on your truck will let you. I have seen trucks spark when they go over even the slightest bumps because the frame was so close to the ground. As for the tires, you can take the wheel wells out and they shan't be a problem. It all depends on how much time, money and effort you want/are willing to put in to it. Have fun with it. Start a build thread and keep us up to date with pics.
Life is hard... It's harder if you're stupid!
Today is a good day to be a RAM owner!