For nighttime entertainment that is not clubs/bars (and Dupont Circle is, FWTW, DC’s Gayborhood), there is theater (off the top of my head, national tours to be found at the National Theater, the Warner Theater, and half a dozen others), movies (chain movie theaters and indies), some private museums stay open later, and there’s always book readings, more subdued clubs, whether you want Jazz, Comedy, Poetry, whatever.
Two good sources:
Washington Post Arts and Entertainment or Sunday Source sections (requires free registration). Mostly established venues.
City Paper, good for other (more alternative) venues.
For both sources, but especially the City Paper, it’s good to pick up a paper copy when you first get in the city (City Paper is free, the daily Post is, what .35? .50?)
For shopping, try the Pentagon City metro stop. You get three malls within a block of one another, pretty much any store you could imagine from the cheap to the ritzy.
As others have said, Metro does not use tokens, but various types of farecards. What I, as a local, use is the Smartrip card. It’s required if you plan to park at a commuter metro station (yeah, I know you won’t), or if you plan to be coming back in the future (you can register the card so you don’t lose any money stored on it if you lose the card itself). The Smartrip card does cost some money itself, I think $5, but it’s solid and secure. Look over the page ataraxy22 linked to for the other options. I’d typically recommend the standard paper farecard, which you put on any amount you want, and it debits as you go along. You can refill the amount at any time, and when you get to the last day or two, can start putting on just enough to cover your fare, so that you exit your trip having spent not a cent more than you had to for Metro use.