MFA for a subset of Users or all?

I am reaching out to gain a clearer understanding of our options regarding the scope of Multi-Factor Authentication (MFA) implementation. Specifically, as an administrator for our business, I would like to know if enabling a new password policy is a prerequisite for turning on MFA.

Additionally, I am interested in exploring the possibility of enabling MFA for a specific subset of our business users as a test measure. 

As an Administrator, I cannot see the policy options to choose a specific group of users or team of users to target MFA to. 

Thank you for your time and guidance.