I'd recommend against using any system where they don't both trim together. You can get a cheap servo reverser for under $20 from Tower Hobbies that will keep that from being an issue. Or, if you use the Futaba 9C or higher, it can be programmed in. One of the reasons I got rid of my 7C was that it would not link the trim, (Why not, Futaba?!!?).

If you move that battery back to the tail, you shouldn't need all that weight. But, if you do, it's fine to have it back there as long as the plane is balanced correctly before you fly it. I can't imagine needing both, and I have a heavier gas engine in the nose. I didn't add any weight at all, just moved the battery back until it balanced correctly.

-Pat