Note that its rainy season Sept-Oct. so ... you really should check weather forecast first.
Angkor Wat itself is just ONE attraction in Siem Reap, Cambodia. well, the most famous one. Just like Zoo is just one attraction in Singapore. You can probably spend one whole day there, from sunrise till sunset. It might get boring in between, just sit around and chat with the monks or other visitors.
There are many many "ruins" accessible from Siem Reap, all within driving distance. Thats what your cambodian friend meant. There are also further places which is a day trip on their own. Too bad, due to the cost involved, we decided to go to only one place, but we think its really worth it afterwards. Thinking back, spending the additional money to go to these further places is definitely worth the time and money, shouldn't stinch on it.
I reckon it takes about 6-7 days to do a go-around to visit most of the major and minor ruin at least once. They have a tourist pass system. for 1-day, 3-days, and 6 or more days, something like that. The pass will give you access to all the ruins, (and you really need it, they do check). Accompanying the pass is a map showing you where all the runins are. However, you should hire a local driver to bring you around. I still have the contact of my mini-bus driver, friendly, and english speaking. the mini-bus is good for a group of 4-6 photographers (with equipment). PM me if you wish.
Its mainly architetcture type of shoot. And some landscape shots thrown in here and there. Really up to your interest. Many street scenes opportunities too. Its so different from Singapore, almost everything is worth shooting.
Wide angle lens is a necessity in a lot of cases. Tripod another must, low light condition in-door. be prepared to shoot ISO 50 or ISO 100 outdoor, and then switch to ISO 400 / 800 as you move indoors.
Good Luck.
