I'm going in mind May (14th-20th). How hot is it during the day? Will I need pants and a sweatshirt for night? Does it usually rain during the day and if so how hard and how long?
You will DEFINITELY not need pants and a sweatshirt! You may want to bring some light pants (khakis) and a long sleeved t-shirt just in case you hit a coolish evening, but it'll be 80s during the day with low 70s at night. If you're the type of person who gets cold easily or is bothered by air-conditioning in theatres and restaurants, you might want to have a light sweater.
Generally, the daily rains don't start until June. If it does rain, it's usually isolated showers that don't last that long. There may be a true "day o' rain" here and there, but certainly not every day.
On the other hand if you are always warm/hot like me. In 2003 we wore short and short sleeve every day and night. It was actually hot for us and we were sweating most of the time. Now don't get me wrong, it was't overly hot.