No, just install it and every time you use a password that isn't in the database you'll get prompted to add it. One of them major benefits though is being able to use large, complex, random passwords. So, it is strongly recommended to switch your passwords over. You can do it as fast or slow as makes sense for you.

You can. Look at the organizations features. For basic use I think it's only like one other person, paid opens this up more if you need it.

Yes, requiring authentication regularly is the default. If you use biometric (fingerprint, etc) this is considerably less burdensome. you can adjust all this in the settings though and use whatever fits you best.