Tony, For the tire valve, air pressure within the tube keeps the Presta valve sealed. To add air you simply unscrew the valve and attach the pump head, which must be a Presta style and pump to the desired pressure. There are adaptors that screw onto the valve to use a schrader valve pump head.

Often the heavy items are loaded in the front panniers and bulky items at the rear. A bicycle is typically a 60-40% bias on the rear when unloaded. Trial and error is the best way to determine what's best for you.

Brad