Siem Reap/Angkor are so firmly on the tourist trail that there is not much "adventuring" in the sense of a Stanley-and-Livingston Africa expedition. At a minimum, all you really need is simple transport there and in between the temples, and a good guidebook with a little advance reading. Everything else (a/c cars, guides, etc. are just more elaborate permutations of the same). My preference is to not go through hotels since the hotel has a big markup (or takes a big cut), but instead just find a pedicab driver and negotiate per day for that day's plan (which is MY plan, not somebody else's plan).

The temple complex is only about 20 minutes from Siem Reap with good (and busy) connector road. It is of course busiest in town and at the temples during the high tourist season Nov-Feb. I find both the town and the temple complex more peaceful and atmospheric in the rainy season Jun-Sept. It is hottest and most miserable Mar-May dry season.