I will be there the same dates! Typically the number one piece of planning advice that many give out is that you should arrive in the parks as early as possible each morning. With the way your trip is structured, it looks like that won't be a possibility. If there is any way for you to switch things around so that you spend your half a day in DLR in the morning, rather than the afternoon/evening, that would be ideal, but with a conference I'm guessing that's not going to happen.
First, I would suggest checking out HydroGuy's
DLR Guide for WDW Vets. It will explain a lot of the similarities and differences between the two places.
Take full advantage of FP. DLR is still using the old paper FP system where you can pull a new FP every 2 hours or after you use your current one, whichever comes first. Take advantage by pulling a new one as soon as you can throughout the night, until they run out.
Others may disagree with this, but I am going to suggest that you forget about going to DCA. Many of the rides are duplicated at WDW (Soarin', Toy Story Midway Mania, Tower of Terror). The one that is really unique and great (Radiator Springs Racers) will have a very long line by that time of the day, and all of the FPs are very likely to be gone. Unless you are really set on seeing this one ride and waiting a while for it (there is a single rider option but this may be a bit of a wait by that time as well), then I would forgo park hoppers and just spend your time in DLR. You can also take a peek at DCA by riding the monorail, which goes through DCA and Downtown Disney, on a loop from Tomorrowland.
DLR is celebrating it's 60th anniversary this year (the actual anniversary is July 17th), so there is a new parade and fireworks show debuting soon. I would try to see the new Paint the Night parade and/or fireworks show at least one of your nights there. I would also suggest Fantasmic!, as I love the show and it is better than its WDW counterpart, but with the limited time you have I think it could be better spent on rides.