I think you're talking about a pretty good plan/plane. APC 17x6 should work nice, as well as the servos you're talking about. Engine inverted so stock exhaust will point down is the only reason. The engine could care less! If you're buying a battery, suggest you consider A123.

Optionally, you could run 2 batteries through 2 switches (providing redundancy) - then power your ignition module with those same batteries. Look into a voltage regulator and an optical switch (used to control power to ignition module from an extra channel on your radio). It's a lot to get your head wrapped around at first, but once figured out there isn't a much better way of going about it, and the cost/weight difference is not that much more than having separate batteries for your flight pack and ignition module.

Some guys are not real happy with the stock landing gear. Changing it out for something providing a little more ground clearance might be something to consider as well.