How many days MC do you take yearly? How many is too many to take?

I take when needed. sometimes its hard to tell esp if you are really sick.

Just take when you need. if you are ill and spread illness to your colleagues, you (when their turn to take mc) and the company suffer

There's no right answer to this. I think it depends on your workplace culture. If everyone takes 14/14 days MC, then I would not feel guilty to take MC as well. Also, do consider taking a career break if you constantly want to take MC for mental breaks from work. In the long term, it is not sustainable.

Some of the more junior staff in my company that all their MC entitlement as part of their Annual Leave entitlement