2. As far as the pace you're running at, don't compare yourself to anyone else. No one can tell you whether or not they're "good" paces - you should know from your past running history.
3. "Shin splints" is actually an UMBRELLA term used by those who don't know any better to cover ALL and ANY injury to the LOWER LEG. I recommend actually finding out WHAT the injury is, or whether you're just feeling the impact from running again, and do something about it.
4. Running is a very catabolic exercise - almost one of the most, if not the most, catabolic activities that you can do. Therefore, if you're trying to lose fat but gain muscle, then running may not be the best option for you.
5. Recomping (i.e. losing fat, but building muscle) is VERY difficult to do, and NUTRITION MANIPULATION is the KEY factor in it. My recommendation to you would be to forget running and concentrate on your NUTRITION - calorie/carbohydrate cycle (do some personal research on it) - and make sure your RESISTANCE training is set up for muscle gain, and if you're going to do cardio, make sure it's short and intense HIIT 2-3 times a week, using modes of exercise that do NOT stress your lower legs.