Either I come up with a new project or I rewrite an old project in the new language.
I used to do those old school language tutorials where we start with how to write a variable, then how to write a function, etc. but I think that's better for complete beginners just starting out.
Mojo is a Python superset, Python is written in C therefore mojo is written in C.
I don't know what that rust library they benchmarked against is but given that they claim to have performed 50% better I would be sceptical. Given that most sources benchmark rust, C and C++ at about the same level.