Just got back from a week in HK. Current weather there between 16-23C, it varies about 4-5C (from highest during day, to lowest during night). Generally if it's not windy, daytime temperature of around 21-23C, you can wonder around quite comfortably in at most a light jacket (or a long-sleeve shirt), especially if its sunny.

But, when you wander into any air-con building, it is colder! Yeah, that's right, indoors during the day is colder than outdoors because our friends from HK love cold air-cons (I think they're probably set around 16C or something like that).

At night, a light jacket is definitely needed as it is definitely on the cold side of cool.

Enjoy your time there, it's a great place to shop

That's nowhere near enough. Typical food court meal will cost you about HKD60 for simple fare. Transport am not too familiar coz I bought the Octopus card (something like Touch & Go), and I never bothered to check how much I spent on getting around. I would say at least HKD250/day to cover basic food (assuming you travel around and eat average food, and not just the absolute cheapest all the time), and add some more on top of that for transport.