Originally Posted by AsiaTraveler

Don't count out IND or other area airports just yet. The availability for the TATL leg may be for a NYC-wherever flight, in which case you're going to have to take a feeder flight to connect to your flight anyway. Of course, it would be really nice to take a non-stop flight out of ORD (possible since you're flying UA), so look at that, but don't discount the other possibilities. Have you checked availability for that timeframe? I realize there are a lot of possibilities, but if there are flights available to one of your preferred cities and back from another, that may go a long way toward making up your mind on which cities you'll visit.

You may or may not be able to swing all three cities on one ticket (actually, I'm thinking you can't. You might be able to do one intermediate flight within Europe, but not 2), but as long as you have the open jaw ticket back to the US, I wouldn't sweat the intermediate transit if you can't get it lined up on the same ticket.