They've made it sound like his first two (out of three) appearances will be pre-superpowers and then the third will be the pilot, essentially, so I assume he'll only be in Starling as The Flash for a short while, then move on to Central City.
I hope it works something like that. Arrow is pretty much good without powers. But even so, just having the two existing in the same universe would be kinda confusing.
I'm thinking that unless the Flash will be the only legit super powered person due to an accident, they're eventually going that way with Arrow. Which could harm the show in all honesty, I like the realistic take.
I also hope that their work on the flash show doesn't worsen Arrow in any way. I don't see the Flash really working out personally, I doubt it will attract the mainstream like Arrow has.