I say have the Deflector imbedded in the front of the saucer section kinda like how the Enterprise-D has a small deflector grid inbedded in its saucer section, used when the Saucer seperates away from the Battle section at warp speeds.
As for Impulse engines, I didn't notice that before Sand. The original sketches don't seem to show any type of Impulse system. I say if your going to add impulse engines, they should be centerlined and not on the Pylons.