I run 3x a week. Depending on what I am training for I may not do any lower body work at all. Right now I am training for my first marathon and do none. My legs just feel dead and terrible if I do. Before I started training I only did about 10 min. of lower body 1x a week.
I also spin once a week, which I think works the lower body very well. Upper body gets worked twice a week. I just rotate my Cathe's in 4 week rotations. Core is done 3x a week.
You will really have to experiment and see what works for you. Don't be afraid to take out lower body if you have to. It all depends on your goals. My legs are strong enough to take me 14 miles (so far) and they look pretty good too.
I don't know why some people can do legs hard 3x a week and I can't. I sometimes get discouraged because I am in good shape and have been working out for a long time. You'd think I'd be able to do that too. Maybe it's all genetics?
Good luck with your running, and definitely sign up for a race! They are fun, fun, fun!
Andrea