Debs,
We have been in May before and are going again this coming May.
The Weather, last time we went was similar dates to this year around 7th-21st, average mid-eighties although it does get a little hotter towards the end of the month and can hit the nineties. Very little rainfall, the odd evening shower.
Humidity not too bad, we went last August and it was too hot for us, hence this time we are going earlier.
We have an Autistic son , so we have to think about pushing a stroller around , we were alright in May but struggled last August.
Crowds, generally not too bad, certainly quieter than peak periods, we tend to concentrate on Universal Studios/IOA and Sea World and we found them all okay for crowds and with the weather not too uncomfortable this helped also. In our experience though some parks like Magic Kingdom are ALWAYS pretty busy.
Opening times, off-peak so generally 09:00 to 19:00, with the odd 20:00 finish on certain nights.
What Flower festival? sorry I haven't got 'green fingers'