1) You can fly a 4-cell receiver pack until it is down to 4.4 V under 300 mA Load
2) Charging will only take about 20 minutes at 1 amp charge rate if the pack needs 300 mAh. Will take one hour if it needs 1000 mAh, etc.
3) The absolute best rate to charge is one tenth of the capacity for 14 hours. But charging at the "1c" rate with a peak detector is OK too. Charging at 2C is marginal. I generally don't charge above 2C because it may shorten the life of the pack.
4) Use the home charger overnight for routine charging when you remember. Save the filed charger for the field or for when you forget to charge overnight.
5) The field charger should work OK with the transmitter pack, as well as the receiver
6) A full charge 4-cell pack (nominal 4.8 V) may read as much as 5.5 or higher for a few minutes in use. A 8-cell transmitter pack may read over 10.5 Volts for a while.
7) You can use either a 4-cell or 5-cell pack in your receiver. The 5-cell will give more speed and power to your servos, but will not last as long. Because of the increased voltage, the system is actually using more amps per minute, so you can fly 20% fewer minutes on a 5-cell pack.