According to Lou Scheimer there were never any ego problems between the cast members during recording sessions, although William Shatner and Leonard Nimoy had a tendency to count their characters' lines and complain when one of them had too many more than the other.
The life-support belts came about simply because the bulky spacesuits created for Star Trek (1966) were too complex to draw. (In the original series, the concept of the transporter had come about the same way: it got the crew to the planet without the expense of filming a landing sequence every week.) Ironically, the belts were never adapted for the later live-action movies and television series because making the actors "glow" via special effects would have cost more than making spacesuits.
Walter Koenig, who wrote The Infinite Vulcan (1973), became the first Star Trek (1966) actor to ever write a Star Trek story. Over the following decades, many Trek actors would write films, novels and comic books based upon Star Trek, and many more would direct television episodes and movies.
Originally, the series was not going to include George Takei, Walter Koenig, and Nichelle Nichols due to budget considerations. However, when Leonard Nimoy learned about this, he refused to join the cast unless his friends were included. Rather than lose the most popular cast member, Filmation agreed to sign on Takei and Nichols. While Koenig could not be included because of the budget, he provided the script for The Infinite Vulcan (1973).
Gene Roddenberry decided in the 1980s that The Animated Series (TAS) was not 'canon' (as the live-action series and movies are) because he did it for the money, and in the hopes of reviving Star Trek (1966) (which failed). He also stated that he would not have let the writers do some of the things they did if he had known that Star Trek would eventually return as live-action in Star Trek: The Motion Picture (1979). For a long time, he prohibited writers of Star Trek-related series, novels, comics and games from referencing concepts that originated from TAS (a wish that Paramount honored). Still, this would silently happen anyway over time, especially after Roddenberry's death in 1991 and a subsequent regime change in Paramount. Some of the writers of Star Trek: Enterprise (2001) even openly disagreed with Roddenberry's opinion on this matter in Drawn to the Final Frontier (2006), where they stated that they regard TAS as a legitimate continuation of the original Star Trek (1966) series, and point out how they incorporated Trek Universe details from it into the Enterprise prequel. Several TAS writers have since called it season 4 of Star Trek (1966), and in 2006, Paramount released the series on DVD (without officially commenting on its canon status). In 2007, TAS was added to the official Star Trek website, which many took as a sign that the show is a genuine part of the Star Trek universe. Regardless of that, several elements of the series have since been retconned in later media, and many consider its status as semi-canon.