Why and how to integrate another founder?

I’ve been working on Data Jumbo for over 9 months, I always thought of bootstrapping it alone because I’m in a niche (at least for now). A friend of mine shared her interest on joining the project. She might be complementary. I see that a lot of companies here have been bootstrapped at 2 or more, and succeeded at it.

What do you think should be the criteria to evaluate if I should open my mind to a multi founder company or stick to a solo business?

How would you share the revenue and shares?