I'd stay away from Nimh with your setup. And 7 Volts are fine for your servos, the rx may not like it.
They don't like high current draws, charging is very slow and if a cell fails, it will open up and you loose your plane. Nicd batteries will shorten out and you may have a chance to save your model with a lower battery voltage.
There are some great Life batteries available now, charge in 20 minutes, they are light and deliver enough current.
How many amps you will draw is hard to say, for scale flying you will be fine with a 5A regulator. If you fly agressive 3D maneuvers, get 8A or more.
This is as safe as it gets:
http://www.hobbyking.com/hobbyking/s...er_System.html
two batteries and regulators. If one fails, the other takes over