Your 6EX transmitter batteries that came with the unit will easily give you at least 2 and 1/2 hours of use. The indicated voltage shown on the LCD will fall to about 9.4/9.3 volts after about 45 minutes and hold above 9.2 volts for another hour easily. It is perfectly safe to fly until the voltage fall to 9.1 volts (about 2 hours and 45 minutes) if starting with a fully charged battery. In fact you can fly down to 8.9 volts (3 hours) safely and still have plenty power to operate your transmitter. Now the receiver is another story, depends on how many servos and how you fly. The suggestion to put a Voltwatch on your plane is an excellent one; IMHO much better than a loaded voltmeter as (if you check after each flight before turning off either the transmitter or receiver, your readings will reflect the actual loads you have been experiencing in flight.
As to batteries, if you have adequate space and weight carrying capacity, stick with NiCads as they are much better than NiMh in all respects except for size for equivalent capacity plus are much more tolerant of abuse such as minor overcharge and heat plus will last for twice as many charge/recharge cycles. In the way we use them in RC, they are no more apt to have any memory problems than the NiMh. For all but the most stringent weight requirements, NiCad still rule the roost.