Is there a way to tell XCode fold methods/functions by default when opening a file?
I don't think so, there are some handy keyboard shortcuts though:
Fold ⌃⌘← control+command+left
Fold All ⌘⌥⇧← command+option+shift+left
Unfold ⌃⌘→ control+command+right
Unfold All ⌃U control+U
Fold Methods/Functions ⌃⌘↑ control+command+up
Unfold Methods/Functions ⌃⌘↓ control+command+down
Fold Comment Blocks ⌃⇧⌘↑ control+shift+command+up
Unfold Comment Blocks ⌃⇧⌘↓ control+shift+command+down
Focus Follows Selection ⌃⌥⌘F control+option+command+F