Is it possible to simply declare that you have started a new religion with arbitrary rules, and expect to enjoy all applicable first amendment protections for it? For example, if your religion just happens to forbid working on Mondays, could you then sue employers who refuse to accommodate you? If an employer refused to hire you because they didn't like that you participate in made up releigion, would that be legal?
My instinct is that the answer is no: Courts would probably view the religion as insincere, even if it was. Without a sizable congregation and a substantial history, it would probably not be considered a "real" religion. However, there have been new religions which succeeded in becoming officially recognized in the US. So what are the minimum conditions required for a religion to be recognized as genuine by the government?