You said your main goal is "losing stubborn belly fat".
Although you can't spot burn fat, if what you're doing now is achieving that goal for you (fat loss in general), and you are overall happy with the results you are getting and the training routine, don't change anything.
Cardio combined with strength/weight training is a great way to burn fat while maintaining lean muscle.
When that main goal changes to something else, perhaps building lean muscle mass, then re-evaluate your routine.
Are you putting too much preasure on your knee's you asked? Only you can answer this. If you are experiencing any kind of pain or discomfort, perhaps you are and you might need to see your doctor before doing more damage. Otherwise, I'd say no. Just make sure you're using good form performing the exercises - for example, if doing squats, make sure your knees are tracking the same direction your toes are pointing. Also make sure you are wearing a good quality pair of sneakers when running - preferably fitted by someone who knows what they're doing. It may also be beneficial to look at getting some Orthotics made specifically for your feet.
Higher reps will improve endurance to some degree but it's not going to do a lot for building lean muscle mass - if that's what you want out of it. It's good to mix it up every now and then though. It certainly shouldn't have any negative effect providing you're not doing it every day - assuming you are actually trying to build muscle.
Fasted training works for some people, not for others. Personally, I can't train on an empty stomach - I feel sick. About 30-45 minutes before training, I have something to eat.
Everyone is different though. If you can train on an empty, it may work for you. In a very basic sense, without going into the intricacies being it, if you've got little fat to lose, I'd be eating. Eating will signal to your body to release/use body fat for energy. If you're not eating, your body will hold onto fat - your bodies own survival countermeasures will be working against you.
This is why some people find it very hard to lose those last few kilos/lbs - they don't eat as much in the hope it will help burn off the extra fat when in fact, they should be eating slightly more. Not only that, but if you go too far, your body may start breaking down lean muscle for use as energy. This is not good! I personally know a couple of people who have pushed themselves to far by not eating. They get sick very easily and they have no muscle tone/definition to their bodies.
Hopefully some of this information is useful to you.