I want to learn more about homomorphic encryption and eventually make a career from it. Currently, I'm thinking to have my bachelor degree in this field. What background should I have for this ? How good at maths should I be? Are there any tests, challenges I can take, programs I can imagine, write, anything I can read to discover if I am suited for it?
I'd say the people dealing in homomorphic encryption are at the forefront of applied mathematical research (Shai, Smart, Gentry, Boneh...). So world-class certainly wouldn't hurt!
Pick up a paper cited by HELib (for one example starting place), read it. Fail to understand it, find a cited paper, read it... repeat until eventually you find a text book instead of a cited paper. Better yet, just start from Shoup's number theory book freely available online.