Hi Vicki!
We have a teenager who plays football and we use it on all his football gear (under and over) and have had great success. Now that we are out of diapers, we do use a fabric softener mostly for scent - Charlie's is unscented and we have two dogs that like to sleep in my laundry basket so I have to fight that off too!
As far as the water softener goes, if you normally need water softener then you probably should get a pack of the Charlie's Booster Hard Water Treatment just in case. We currently have the Hard Water Kit which includes a 100 load pack of laundry powder and 1 pack of the Booster on sale.
The 1200 Load is definitely the way to go if it works for your teenager, but I recommend starting with the 100 load to try out. Give it 3 or 4 washes with Charlie's to make sure any old detergent that is stuck to the fibers and possibly trapping odors gets washed out.
As far as how much to use on your front loader, you use 1 scoop for a normal load which is about 1 tbsp. Add a little more for a large load or less for a small load. It seems like it is not enough because it is such a small amount, but it is! Everyone's water is different so you need to pay attention to how your laundry is coming out, but it doesn't take much to get it optimized for your location!