So. Cal weather is hard to predict. I remember in 2004, we went that time (late April into early May) and it was extremely hot. We had several days in the high 90's, thankfully it wasn't humid at least. We went that same time a couple years later and it was much cooler. We needed jackets in the evenings but the days were warm.
Any weekend, any time of year at DL is crowded. But for your weekdays, you should have very doable crowds, especially first thing in the morning. So be sure and get to the parks right at opening. Because even during the most crowded times, those early mornings are heavenly.
Have fun!