Starting next week i am going to try a run 3 to 4 times a week with rest days in between. These runs will be alternating...

8x100m sprint then jog back (fartleks?)

1.5 mile best effort, 5-10 min rest, 1 mile best effort

5 mile steady 80% best effort

Has anyone got any advice as to how I could ...

Would there be any major problem in doing weight training for upper body, alternating with cardio sessions for the lower body on the off days (running, etc.), or would they cancel each other out as tom123 suggests?