This time of the year usually a well placed citranella candle or 2 will ward off the no-seeums. Given that we expect to have dry, cool and an light breeze I expect them to be managable. Come July is a whole different story all together.
As for rolling thunder, they do not close all of DC just some roads. I have never once had an issue getting in or out of DC, but avoid the area around the National Mall with a car. So only expect road closures on both sides of the mall. If you stick to K Street, 395, 695 and 295 you will not notice the traffic other then when the bikes all head their seperate ways once they leave the tidal Basin.
Rolling Thunder will meet up at the Pentagon North parking lot and then run the route from there. The route is from the Pentagon North Parking lot, up Washington Blvd and across the Memorial Bridge onto Constitution Ave eastbound to Pennsilvania Ave, they ride that to 3rd Street and South to Independance and finish up at West Potomac Park.