Joss Whedon had a five year plan for the series and had already worked out how the characters will evolve over time but the show only ran for two seasons. With this in mind, you can see how the plots of season 2 could have been spaced out to four seasons.
DOLLHOUSE is part of a FOX campaign called "Remote-Free-TV", which also includes fellow-FOX-show FRINGE. Both shows are expected to have dramatically reduced commercial breaks and therefore more actual screen time.
Season One is 13 episodes long, but only 12 were actually aired. The reason for this is that the original pilot was scrapped (the other episodes being altered accordingly), leaving 12 to air on TV. However, the series had already been sold to foreign markets as a full 13 episodes. To accommodate this, an extra episode was produced at half-budget: "Epitaph One" takes place in an After The End scenario, stars Felicia Day of Dr. Horrible's Sing-Along Blog (2008) and The Guild (2007) fame. Epitaph One, as well as the original unaired pilot "Echo", have both been included on the Season One DVD.
The company behind the doll houses in the show is Rossum. As confirmed in episode 2.11, this is a nod to Karel Capek's play R.U.R. (Rossum's Universal Robots). The play deals with artificial people, programmed to do work who eventually turn on their masters. This play also introduced the word "robot" into the English language.
In the season two episode "The Attic," Enver Gjokaj's identical twin brother Demir Gjokaj plays a alternate version of Enver's character who fights "himself" while trapped in a dream. This was actually the second time in his showrunning career that Joss Whedon cast the non-acting identical twin brother of one of his series regulars as a supernatural double or doppelgänger of the regular character; the first time was during "Buffy the Vampire Slayer," when Nicholas Brendon's twin, Kelly, played a part of Xander's personality that had become mystically separated from the original Xander.
The show was originally more focused on the sexual aspect of the characters, but Fox was worried that the Dollhouse theme and their clients would resemble prostitution, so they pushed Joss Whedon to make it more a thriller.
15 years earlier in 1994's "True Lies", Eliza Dushku's character Dana Tasker is the daughter of Arnold Schwarzenegger's character Harry Tasker, whom is a secret agent. Echo (Eliza Dushku) is a secret agent.