How to optimally care for bags?

I am absolutely new in the handbag business and never really owned expensive leather handbags before. I want to care for them as good as possible so I don’t ruin them but have no idea how exactly.

Does one use protection spray on them?

Storage in dustbags (i‘m in Germany if that makes a difference)?

Storage in the box? I read that it’s not good bc the leather can’t breathe?

How often should you use leather cream? How much of it? Can you destroy a bag with leather cream?

Anything else i need to know?