Q: Should I encrypt my backup disk?

I don't have any sensitive information on my computer, so I don't really see any need (unless people could somehow steal an identity from holiday photos).

1) Does encrypting the files mean, if I upgrade my OS X or anything like that, my computer won't be able to read the files?

2) Will I need a password if I encrypt the files?

3) Does encrypting files take up more storage on the backup disk and/or my computer?

4) Does it take longer to back up my computer if I'm encrypting files?

Thank you for any help given