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.
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 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.
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.
The super connectivity of the world of Joss Whedon strikes yet again: Edward James Olmos (mentioned in the Pilot episode but not actually a cast member) would go on to play a character on Marvel's Agents of SHIELD along with other Dollhouse alumni, Dichen Lachman, Reed Diamond, Amy Acker, and Patton Oswalt. Not coincidentally, that series is also written by Joss, his brother Jed Whedon and sister in law Maurissa Tancharoen (who appears in 3eps of Dollhouse as well as Dr. Horrible). Additionally Enver Gjokaj had a small role in Marvel's The Avengers, also directed by Joss, of which SHIELD is a spin-off series. He was also in the Agent Carter series, which connects to the other Marvel series and films. You can also find numerous actresses and actors in Dollhouse from Whedon's previous shows and future films; Eliza Dushku (Buffy the Vampire Slayer and Angel), Amy Acker (Angel, Cabin in the Woods, and SHIELD as mentioned previously), Summer Glau (Angel and Firefly), Alan Tudyk and Mark Sheppard (Firefly), Felicia Day (Buffy the Vampire Slayer and Dr. Horrible's Sing-Along Blog), Fran Kranz (Cabin in the Woods), Keith Carradine (Angel), as well as others I'm sure. Fran Kranz and Amy Acker would work with Whedon again in Cabin In The Woods, which also stars Chris Hemsworth, Thor himself, for another link back to Joss. In short, it's extremely common for Joss Whedon to cast actors/actresses he's worked with previously and use them over and over again in both his series and films.
Summer Glau joined the series following the cancellation of Terminator: The Sarah Connor Chronicles (2008) which was based on The Terminator (1984) films. Eliza Dushku starred in Terminator creator James Cameron's True Lies (1994).
The series had a similar premise to the earlier television series Joe 90 (1968). In that series Joe McClaine, a preteen secret agent had skills downloaded into his mind which enabled him to become anyone.
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.
Eliza Dushku was James Cameron's original choice for the role of Max Guevera in the TV series Dark Angel (2000). The series was about a genetic engineered woman, whom was created and trained by the US government as a soldier and an assassin whom escapes from a lab whom moonlights as a courier in the post-apocalyptic world as she searches for other genetic engineered men and women whom also escaped from the lab.
Olivia Williams later star in Hanna (2011) as Rachel. The film is about a girl (Saoirse Ronan) trained as an assassin by a Ex CIA operative (Eric Bana) whom discovers she was created in a genetic experiment to create super soldiers.
After stealing Rossum's dossier on Bennett Halverson, who is played by Summer Glau, Caroline reacts to the woman's impressive intellect by commenting, "I bet you could kill me with your brain." This echoes a line from Glau's earlier show, Firefly, in which her character, River Tam, threatens her shipmate Jayne by saying, "Also, I can kill you with my brain." Both shows were created by Joss Whedon.