I agree with everything that Al has said. Running a small gasser on NiMh with analog servos shouldn't be a problem with current delivery. With larger airplane with much higher current requirements NiMh would be a poor choice.
There are are many ways to electrically set up our airplanes. Most work just fine, some are better at optimizing reliability and others are good for optimizing performance. My personal preference on battery chemistry is LiFe for an unregulated setup and Lipo for a setup with a regulator. The reason for that is I want consistant voltage going to the servos. This makes a setup that responds the same from the first flight of the day and the fifth. When I get to a certain size airplane I go to a regulated system to get away from mechanical switches and be able to use big batteries. My 40% Extra runs dual 5 amp Lipo batteries. There are new smart switches available now that do not require regulators but as stated, the regulation is more to keep a constant voltage going to the servos. An unregulated system gets LiFe batteries due to their flat discharge rate so from first flight to fifth there may be a half volt drop at the most before I top off the battery.
As my personal opinion, for your setup I would run dual 1500 mah LiFe 6.6V batteries into your switch with both outputs going into the RX. I would then be mod the opto switch and run ignition voltage through the RX so you can cut the ignition from the TX. I have found that by not using the throttle servo to shut the engine down the servos last much longer. In the event of a servo or linkage failure you have the ability to shut the engine down and land, some clubs/events require an ignition kill via TX as well.