What is Lost In Upgrading?
 

I am on vB 3.7.2 with blogs and flashchat.

I want to upgrade to 3.8.4.

However, will I loose the following when upgrading:
- The plugins like will they stop working?
- The files in the forums folder will they be deleted?
- The style edits, will they stay.
- The templates I have added to the forums, will those stay?

I don't want to loose that stuff. How is that prevented?