We took two hours. Earlier was better. But start of the day was very busy. Half an hour after opening. Do some reading before hand, it makes it even more interesting.

$45 adult, $25 child, $120 family full details on website

Often busier on Saturdays and with Floriade on, I would expect that it is more busy than usual

You can buy tickets there only a few people in the que when I went on a friday afternoon

I don't know -- we drove.

there is no general entry cost but special exhibitions do have entry fees. these fees vary from one exhibition to the next.