Hi.
yes (as long as you have your vault files available)
no
The masterkey file is part of your encrypted vault and is needed to unlock it in combination with your vault password. (it is crucial for your vault, do not delete/move/rename it)
The rtf file “important.rtf” that is stored in the same folder as the masterkey files is not encrypted and is created to explain what you see in this folder, and that you should not rename/move/delete/copy anything from/to it. This is not where you store the files you want to encrypt. This is just the place where cryptomator places your encrypted files. This is the folder you want to sync to your online provider.
When you unlock your vault with your password, a new “drive” is created. There you can find a file “welcome.rft” This is the place where you want to store the files in, that you want to have encrypted.
(as described in the rtf file)
PS: remember to do backups of your files. If your loose access to your vault (for what ever reason), there’s no way to decrypt the files anymore. Just like it is with any other encryption solution.