Going back to Mavericks: will i lose my files that I have created on Yosemite? FileVault slowed my MBP. So, I am going back to Mavericks.
How can I make sure that my files saved on Yosemite will not be lost?
If I go back using Time Machine, how do I access my files that were saved on Yosemite?
Do I have to make copies of all these files on a separate flash drive bf going back using TM?
Going back to an older TimeMachine backup will make your other files deleted.

You will have to backup them to another place where you can later access them, because using TimeMachine is kinda like using well.. A time machine.