We've been in May the previous 3 years (I think it's 3). Weather wise is very pleasant, mid 80s to mid 90s but without being humid like the summers. We've had really good luck & had probably 5 showers across our 8 weeks being there in May, but I would call that good luck not the norm.
Crowds are good. It's usually in the 4/5 region on the crowd trackers, with a little planning & good FP+ use we queued more than 20 minutes only once or twice the whole vacation(s).
Star Wars Weekends usually make DHS busy Friday-Sunday but don't affect the other parks, just be sure if you can to get in & out before Presidents day which is the end of May I think, it gets crazy that weekend.