My wife, daughter, granddaughter, and I had a wonderful stay at Teresa and Reid's downstairs apartment in the lovely DC Cathedral neighborhood. The bed my wife and I slept in was very comfortable, and the kitchen was a cooks delight. Coffee, tea, cereal and milk were supplied by our friendly hosts, which we greatly appreciated. If you do plan to cook in, I would recommend you bring basics with you so you don't have to run out and shop, though our hosts will do shopping for you prior to your arrival if you choose. One thing I did learn while shopping at the new Giant grocery on Wisconsin avenue is that there lower level parking is free only for 30 minutes, but if you stay longer, you can only get out by paying with a credit card. There was no information at the payment exit on what to do; cash is not accepted.
We arrived in DC during the Cherry Festival and found free parking difficult. We did learn that you can park free at the Capitol Building parking lot on weekends even though signs say "permit only". I'm not sure when Congress actually works, but it's surely not on weekends.
If you do drive to the National Mall area and plan to leave when the museums close, I would not follow the advice of your navigation system. Constitution and Independence avenues become gridlocked, and trying to make any turns is nearly impossible with all the pedestrian traffic. Instead, I would just head north on one of the numbered streets( 3rd for example) and zig-zag your way to Massachusetts Avenue and head northwest to the Cathedral district. I say zig-zag because of one-way street possibilities.
If you don't drive into town, transportation from the apartment is easy. Buses to Georgetown and area south can be picked at Garfield and Wisconsin, and buses to Dupont Circle and a block short of the White House at Garfield and Massachusetts.
If you plan to tour the National Cathedral, fees of $11 and $7 dollars are charged Monday through Saturday. Why not go to church on Sunday?
My granddaughter's most memorable visits were to the Holocaust Museum and the Ford's Theater tour. You must have tickets for both of these. You and get them online for a specific date and time(fees are charged), or you can take your chances and pick them up for free in person. Ticked are for timed entrees.
The American Indian Museum had a great cafeteria serving interesting native foods, and the cheapest way to eat at the Mall area is to visit one of the many food carts which are plentiful.
Enjoy your stay, we did.