6. Heavy weight and low reps or light weight and high reps?
It all depends on your goal. Anytime you put the body up against a resistance (weight) it has to adapt and change (grow or shrink). You want to be able to push moderate weight for long periods of time? Then go low weight and high reps. You want to be big and powerful for short periods? Then go low reps and high weight. You want the best of both worlds? Then train both ways.
I like to diversify my training as much as possible. I also like my training to be functional. What's functional? Functional is training for real life. I want to be able to get up and down off the ground with ease. Therefore, I do tons of burpees. I want to be able to lift things overhead, and I want to be able to pick things up off the ground without throwing my back out. Overhead presses for shoulder strength and dead-lifts for lower back stability are great for this.
Most of my bodyweight exercises develop core strength that helps to keep you injury free in everyday life. For examples of functional workouts I create for my Troops that I train, check out my "workouts" board on Pinterest.
5. What is the best form of cardio?
I'm going to quote a friend of mine Dave the Fitness Manager @ the Transit Center Manas (Kyrgyzstan) on this one. He said something to me that I will never forget and will always use. (Paraphrased) "The best (exercise/equipment/workout) for YOU is the one you will do! I could tell you running, jumping rope, swimming, or 300 other cardio exercises that are available. The best one is the one you enjoy. The best one is the one you will do."
Personally, I love intense cardio exercises that get my heart up high. These burn the maximum amount of calories in the shortest amount of time. That's what we want right!? Who wants to toll away at an exercise for the benefits you can get quickly with another? Exercises like the burpee and the mountain climber accomplish this with max effort and minimum time and replicate the intensity of sport and who doesn't want to feel and look like they did when they played competitive athletics?
Get in the gym, or living room, or outside and get your heart rate up. Get creative, get active, and remember to have fun with it, or it will seem like a mundane task that you HAVE to do, instead of WANTING to do.
Get after it!