I can only comment on the Siem Reap portion. I would allow at least 3 days in Siem Reap. This allowed us to visit a lot of temples, plus the floating village. We would visit temples in the morning, eat lunch, nap and then visit more in the afternoon. I'm not normally a napper, but did I ever appreciate these naps.

We stayed in a small guesthouse for around $45 a night, so not really upscale, but it did have aircon which is all I cared about.