You should be fine for a 1 hour race with 1200's.
I know that Spektrum and digital servos do draw more power than analog stuff, but I ran a 1 hour main along with a few minutes of warmup on a 730mah battery. This was using all airtronicsanalog gear. I have made 1 hour with an 1100mah battery using a single futaba digital, analog throttle servo and a spektrum system.
I see no advantage to a lipo receiver pack. I would not get the lipo receiver pack and if you use them you should get the voltage regulator.