well, that's very sensible of you, but I think you can afford to be a bit more adventurous than that.
in order to get any real benefit out of the weight training i would advise (after you get your form down) that you aim for lifting as much weight as you can. so if you are doing 3x10 you should be doing enough weight that at the end of each set you are really challenged to get the weight up. as time goes by the weight will have to increase and you will see the strength and performance benefits form lifting. lifting low weights really isn't going to give you a lot of benefit. as for your reps getting smaller or injuries i will say that you will get more benefit from really challenging your muscle on 8 reps than you will from the light weight for 50 reps. and muscles are designed to do work, you aren't going to injure yourself if you do the exercises with proper form. you will be sore but the more often you lift the quicker your body will heal from its soreness.
My advice is to select a weight that leads to failure at the end of the last rep of the last set. This means you literally will not be able to do any more on that lift and would have to wait a long time before repeating the lift.
after reading i'm considering replacing my cardio training with tabata training something like a 12/16 minute tabata training work out.
also i find running boring and compared to tabata training it apperently even is less effective for fat loss http://www.squidoo.com/tabatatraining talking about eyeopeners ej
