Wolfie - if you keep all your questions in one thread, then it'll be easier for people who'll be taking the time to give you ideas to keep track of what you've already been told.
Personally, after a long trip I'd try and relax a bit for the first full day. How about hiring a tuk tuk and visiting the Killing Fields, S21 Genocide Museum, perhaps the Russian Market, and finishing the day off at the FCC (Foreign Correspondents Club) for the Happy Hour between 1700-1900. Great views from the balcony to over the river, and the chaotic traffic on the Quay below.
Early night, and in the morning get the 0845(?) Giant Ibis bus to SR. Arrives in SR @ 1500.