Castelli Gabba range is probably the top of the line stuff simply because it doesn't keep the heat in while keeping you mostly dry. It's expensive stuff and there are a few cheaper competitors but it's hard to go past the original Castelli stuff. You could also look at the Castelli Perfetto jersey for warmer weather. While we are talking Castelli you can also look at the nanoflex arm and leg warmers and bib shorts. The fabric is not completely waterproof but it does repel water.

I live in a sub tropical climate and keeping dry during the occasional bit of rain is nice but using a cheap foldable rain jacket keeps me dry only until I start sweating like a pig (which can happen within minutes). In very cold temperatures that's not as much as a problem but as you live in Hong Kong I imagine you'd want to avoid those types of rain jackets.

Shoe covers would be essential for extended rainy riding otherwise you will end up with shoes full of water.

It depends on how dry you need to be.