Most futaba gear is happy with a five cell pack except the gyros and some of the digital servos. They specifically warn against using 5 cell packs. You can use all the other futaba stuff without any trouble or regulators. If the lithium cells were only 7.2v you could get away with that also but when a lithium polymer 2 cell pack comes fresh off charge it is at 8.4 volts which is too much. The rx will be real jittery and unstable.
I run five cell packs in all my planes and four cell packs in my helis due to the gyros and digital servos.
I use several different chargers but I like the Hanger9 sure cycle which can handle 4 or 5 cells. There are lots of chargers that can do the job though.
basmntdweller