Re: How much running is too much?
Everybody's already covered some solid guidelines for including running in weekly training, but I'll add this:
You mentioned that you've added running to what you were already doing. Was what you were already doing working? Were you getting stronger? Faster? Improving cardiovascular and muscular endurance? Recovering adequately and keeping joints feeling healthy? If you can answer yes to all of these, then adding running to your weekly regimen is not going to a problem at all. If you answered no, then you need to take a step back and reassess.
It's all too easy to add more to our current training without taking into account that adding more stressors will definitively require more recovery. If you weren't recovering like a champ before, you either need to a) remove something else from your training; or b) up your recovery game (sleep is probably a great place to start). Otherwise your progress is going to halt or start sliding backwards.
That being said, I'm willing to bet that a few miles of running every week isn't going to make a huge negative difference in the long run (hah).