General rule of thumb on things like this: if it was produced with it, it needs to be there...
Not sure on the roll bar thing, but If I was in one and I rolled, I would definately want it in there.
Windshield- definately need goggles- I have a few friends that do it regularly.
Mirrors, if it had 2, you need 2. Lots of guys have come up with creative ways to add them to where the door hinges were/are.
That's my $.02