Sharepoint

Dear Share Point admin and all member in this community, 

Good morning, as I am a freshman in here and I am willing to learn more about Share Point. I have some questions that I think you all can answer it for me as I research a lot about it but cannot get answer. Questions are these:

1. How to make the folder read only, but the content in the folder as editable.
2. How to prevent user from downloading files from Share Point online, If user can download files from Share Point online, how to prevent them from sharing it outside.
3. Will any changes in the files and in the permission of Share Point online be reflected on One drive offline client.

I am thankfully and waiting for your answer.