I think trying to see both parts of Universal (Studios and Islands of Adventure) in the time alloted for the excursion would be a real push and not too much fun. A lot of people on the various boards I visit have chosen to do this on their own. But I agree with what disneylynn said. I have read express passes (worth it) are cheaper at the park. Mid-April may not be too bad since you will be missing Easter and most Spring Breaks. Can't honestly say about the weather.