RE: knee trouble from running
You're a big fella, so I would suggest getting shoes that are up to taking that kind of impact. Perhaps seek out a running shoe shop specialist. They'll also be able to check your running style to find out if you need special tech in your shoe (if you're an overpronator for example), or perhaps you could benefit from orthotics.
Where running's concerned you've got to get the right pair for you, it can make the difference between running injury free and not.