I run two receiver batteries through a smartfly super regulator, with their miracle switch. The super reg will isolate the bad battery if it occurs. and regulates to 6 volts. It also continually jumps from one battery to the other drawing them down in equal amounts. 7955 is not a high voltage servo and may have issues with unregulated A123 voltage. I don't know if that is an issue for the 7955. If you will use the receiver battery for your ignition, you may want to buy a Ignition Battery Eliminator Circuit, which filters ignition noise that may effect the receiver. By the way, twisted servo extensions are twisted to help eliminate interference, which to my knowledge was of particular concern with 72 mhz radios. I fly with a DLE 55 and a stock muffler. Many still use a tuned pipe but some feel the increased power of a pipe comes at a cost of inconsistent throttle response. Seven channels is plenty if you use a manual choke; I think most use a manual choke for this reason. I do and it works fine. Any standard digital, metal gear servo would be fine for the throttle, with ball links at both ends. One suggestion, if you are new to gas try using a chicken stick. These engines are powerful and can cause injury. The stick may save a finger or two. I have used a stick for some time and find it very convenient and after a couple of flips it felt very natural and stores in my pocket. I have over 370 flights on my Yak and love it. Every one is nervous when they start out. Get assistance especially for your first flights. By the way, Tower has a great online manual for the DLE 55 and it is worth reading. The DA 50 and 3W manuals are also worthwhile. 3W gives detailed breakin instructions. The following is a great thread for gas engines. It is extensive and pretty much on the mark.
Incidentally, most 50cc planes are set up the same basic way. If you don't understand an issue in the EF manual, check out 3D Hobby Shops online manual. It contains some good tips.
http://www.rcuniverse.com/forum/m_86...tm.htm#8673009