Hi, and your question is a great question.
I will tell you that if you can plan into your trip, plan to be in the park Monday to Friday. Still I go on Saturday and Sunday, it is only a bit more crowded. One cannot compare HKDL to WDW, night and day is the best way I can put it.
The weather is another issue. Hong Kong summers are hot, humid, and rain rain rain. There really is no spring and fall, but we like to pretend here that there is this time of year. It is funny, the leaves do not change colour, they just fall off the tree. Thus the winter time is the best time of the year. Hong Kong weather during the winter is cool, dry, and sunny everyday. If you allow me to suggest, I really like September, through to January. The Halloween party that HKDL puts on is really fun, and the locals really get into the action. Christmas is less and less every year as the mainland Chinese do not celebrate Christmas. I would also suggest that you stay clear of the month of February as this is the Chinese new year celebration, and HKDL is a nut house. I do not go to the park any time during the month of February.
I hope I have helped a bit, but please do ask questions.
It's the magic at Hong Kong
Disneyland, enjoy!