Definitely. TMNT started as a comic. Its success in the comic world led to its adaptation into various forms of media. The comic version was the original source that sparked the franchise.
The origin of the Teenage Mutant Ninja Turtles is really interesting. There was this mutagen that was created. Four turtles happened to come into contact with it in the sewers. Along with them, a rat was also affected by the mutagen. This rat, Splinter, had been observing the ways of ninjutsu from his owner before the mutation. After they all mutated, Splinter taught the turtles ninjutsu. They grew up in the sewers and became the Teenage Mutant Ninja Turtles we know. Their existence was soon discovered by April O'Neil, and they got involved in various battles against the evil forces in New York, especially the Foot Clan led by the menacing Shredder.
The availability of Teenage Mutant Ninja Turtles comics online varies. Sometimes you can find them on official comic publishers' websites, while other times they might be on third-party platforms. Just need to do a bit of searching.
Definitely not. The TMNT franchise has a wide audience that includes children and families. Fanfic that involves 'gay ninja turtlecest' is not in line with the family - friendly nature of the series. The fandom should focus on positive and respectful interpretations of the characters and their relationships, like their loyalty to each other as brothers and their fight against evil.
One idea could be a story where the Teenage Mutant Ninja Turtles discover a hidden mecha technology in the sewers. They have to figure out how to use it to defeat a new, powerful enemy. Maybe it gives them new abilities like enhanced speed or the power to fly.