Scott,
Please pardon my emphasis here, but I cannot stress these basic points enough. The best thing you can do as a beginner or "retread" is
KEEP IT SIMPLE.
DO NOT OVERTHINK THINGS. The more things you try to change, the more potential headaches you set yourself up for.
The Galaxy will fly just fine on a
bone stock LA-.25 and is a great choice. I'd suggest a 9X6 prop, that's what I use on them, but a 10X4 would probably work OK too. Just do like Doc says and focus on building the plane as straight and as light as your abilities allow. The better aligned your model is, the better it will fly, period. Weight is also a concern, always keep it in mind, but straight will help things immensely. Also focus on setting up a nice smooth operating control system. For general and/or beginner purposes, the ONLY reason you would need to change out the remote NVA is if you don't have enough room for the fuel tank. I have run many LA's with the stock remote NVA and unless damaged, they work just fine and are actually very user friendly. If you
do decide to change it out, use the one Leester suggests above from Tower Hobbies, easy to obtain and they work well. It's a factory O.S. item and you can still use the stock venturi with it too.
There are a bazillion different opinions on all this stuff, but until you learn what
you like, you will typically be wise to revert to basics, and K-I-S-S.
