Yes, look in the app manual on how to archive. Save the archive folder and also your custom profile folder if you made any of those. You can save on cloud or some other location on your device that's separate from the app's document folder.
You shouldn't have to reload the app. You can always just update from the app store and your data will remain intact as long as you don't remove the app.
When you block a person, they can no longer invite you to a private message or post to your profile wall. Replies and comments they make will be collapsed/hidden by default. Finally, you'll never receive email notifications about content they create or likes they designate for your content.
Note: if you proceed, you will no longer be following .