You can work on both your sprint speed and endurance. It is foolish to train like a sprinter for a few years and then mvoe up in distance.
I would spend the Fall months doing the following:
Running:
4 days per week: 1-2 easy runs, with form drills (high knees, butt kicks, etc.) and light strides
1 day per week: Hills. Solid surface, not too steep a grade. Start with 12 x 200-300 meters at 3k-5k effort for a month, then 6-8 x 400-600 meters for a month, then 4-5 x 800-1k uphill reps for a month. Then a month at 400-600m reps a little faster, and a month of 200-300 even faster. You'll be amazed at how much power you have after doing lots of hills. All the great 800 runners did a lot of hill work. Look at Seb Coe's development: hills were central to his early development.
1 day per week: Something to stress the aerobic system. Alternate between ruise intervals (6-8 x 1k at 5k pace plus 15-20 sec. per mile with 200 jogs), tempo run (20-30 minutes at 5k pace plus 30 sec. per mile), and long intervals (6-8 x 800 at 3k pace with 400 jogs).
1 day per week: Train like a sprinter. Warm-up. Lots of drills. 2 x 20m, 2 x 40m, 2 x 60m, 2 x 80m with 3-6 minute rests, all at 90-100% full speed. Cool down.
Other:
-Core work 3-4 x per week.
-Upper body and lower body lifting 2-3 x per week.
-Plyometrics 1-2 x per week. Start easy and progress. Start with simple bounding drills and simple one-leg hops, progress from there. You shouldn't do depth jumps for awhile.
-Pool runs as much as possible (30 minutes per day will do a lot for your aerobic fitness)
-Preventative icing