This is an oxymoron if you ask me. I honestly don't understand the "flat bar road bike" thing at all. Making a modern drop bar bike comfortable and more upright is much cheaper and easier than than converting a modern flat bar bike to drop bars. With a 4 mile daily ride, having multiple hand positions is probably not important, but if the bike is going to be used for longer distances at any point it will be.

Interrupter brake levers are cheap to add and a few drop bar bikes (The Kona Jake for example) come with them.

If it hasto be a flat bar bike, something with 700c wheels definitely.