FAQ

The film is loosely based on "The Infinity Gauntlet" storyline in the comic. But for the most part, is an original story made for the film. The story in the comic had Thanos wipe out life to please the personification of Death, but failed to do so. Thanos in the movie seeks to wipe out life because he thinks by doing so he can save the universe from overcrowding. Endgame is the final confrontation with him when he seeks revenge for the Avengers trying to undo his work.

No, but it is HIGHLY recommended. This movie is the penultimate culmination of all the 21 movies of the MCU, and if you decide to watch some of them, you may not understand the storyline because they're deeply related to other movies. Like if you watch Captain America: Civil War (2016) without watching Ant-Man (2015), you'll be confused by Ant-Man's sudden presence in Civil War. Also, if you skip Guardians of the Galaxy (2014), you won't understand Avengers: Infinity War (2018). Due to the interconnected nature of the MCU, every movie is important to fully realize the complete picture.

No.

Could be he was referring to the Tesseract as it has played a key role in the movies going back to Captain America: The First Avenger (2011). Or highly radioactive material.

Then again, considering how much "mad science" was going on in that place, it could have just been a generic bluff since Rogers didn't give too many details.

Banner explains that after Hulk was defeated by Thanos, he took the time to figure out how to meld the mind and the muscle together. Essentially putting the mind of Banner in to the body of Hulk.