#1: "Tabloids" are newspapers that often appeal to people who have little education. The phrase #1 says that the literary quality is low. #2: "secured" here means "found". #3: "has got legs" means that once it is published, it is so good that it will keep going (and its popularity keep growing) on its own.

"Tabloid fodder" means it's something that tabloids could write about---usually to make fun of something, publicly humiliate someone, or gawk at something strange. "Tabloid" means a trashy kind of newspaper with no real journalistic standards. "Ripe for tabloid fodder" here means that the subject of the sentence would be a good topic for such a tabloid to write about. "Secure" can mean just "get" or "acquire", or to sort of "set something in place". That is what it means here. "has got legs", or otherwise "[something] has legs" in this context means it will sell copies, it will be successful. I'm not sure why it means that. It's just a known phrase.

Has got legs probably is a shortened version of "have legs to stand on". Something that will last, is sturdy, or you have evidence to back it up. In this writing, it means something that will last. Flash in the pan is the opposite: It will likely disappear and will not have any lasting effect. An example of the saying legs to stand on: She keeps arguing, but she doesn't have a leg to stand on.