Thanks so much rankourabu. (Sorry for the slow reply--didn't get a notification from flyer talk.) This is super helpful. A few questions for you:

--I called United and they said that the first leg as you described wouldn't work as an open jaw because Colombo is area 3 and Dar Es Salaam is area 2. However, when I did an Advanced Search on United.com for those three legs, it does seem to work, although it's 82.5k miles, rather than 72.5k. Is there a trick to getting the 72.5k? Is there really an issue with it being an open jaw as the customer service rep said?

--If I want to upgrade some of the longer flights to business, am I better off booking them as Business Awards when I reserve, or as Economy and then upgrading later (or is it the same number of miles either way)?

--We have 2 adults and 2 kids traveling with 550k miles in my United account and another 250k Chase points which I could transfer to my United account, transfer to a new account at Singapore or ANA (or elsewhere), or book directly from Chase. Any suggestions for the best approach here?

--We actually have several other stops that I was originally thinking I'd need to pay for in cash, but given the mileage savings with what you mapped out, I'm now wondering if there's a way to do more of this trip with miles, and which ones would be best to do as awards vs. paid for. Ideal scenario would be: SFO-BKK-Siem Reap, then (overland back to BKK) BKK-CMB-Jaipur-CAI-IST, then (ferry to Greece) Athens-TLV-DAR-TNR (or vice versa with the two africa stops)-SFO. How's that for a challenge? Appreciate your suggestions!

--Any tips for how a newbie like me could best figure this stuff out myself going forward? On the United.com site, one of the other airline sites, etc.? What are the major considerations in figuring out the most cost effective configurations in terms of award mileage for a trip like this?

Thanks so much!!!