Not sure about locking the exposure in live view. Can you use exposure compensation to get it back where you want? Don't have live view on my E-500 so maybe someone else can help there.

The idea of the ISO limit at 400, is because images will become noisier/grainier at ISO 800 and ISO 1600. If you're happy to live with that, then just remove the limit altogether in the settings menu. Personally, I never use the auto ISO setting. I leave mine set on ISO 100 for best results and then I change it only when I really need to get the shutter speed higher. It's almost instantaneous to change it anyway.

Oly lenses twist that way because it makes the world look nicer!