If you do transit IAD, you would follow signs for connecting passengers not the terminating passengers (sent to the main terminal). Connecting passengers go downstairs below the mid-field terminal and get processed. If you check luggage, you'll have retrieve and recheck it there.

When done, you go back upstairs into Terminal C. UA (mainline, TED and some of the express flights) operates from Terminals C/D. These are connected, but it can be a lengthy walk. There are 3 RCCs at IAD. One around gate C7, C17 and D15 (??i think, not sure of this one??). They are all similar. It's most likely you'll be at C17 or D15 as those are close to gates used frequently for TED flights. There are no showers and is no arrivals lounge, limited food (very) and they charge for alcoholic drinks.

Are you a *G ? How are you planning to get access to the club as they are very particular about letting folks in (and sometimes rude). The clubs aren't that great other than a quiet place to wait outside the hub-bub of the general terminal.