I'm hoping to travel from Hong Kong to Angkor Wat in May and have a few questions:
1) Is this a horrible time of year to go?
We went in mid April and it was fine. See http://asiaforvisitors.com/cambodia/...w-weather.html
2) Is it best to fly to Phnom Penh?
No, fly into Siem Reap. There are very good flights from Bangkok.
4) How much time should I spend in Angkor Wat - is a couple of days enough?
Two full days is the minimum I would recommend. It is well worth the trip and makes Machu Picchu look like a pile of rocks. Enjoy.