I, personally, started sling hunting foxes at 10mm, but it was painfully slow. A good level would be 20 or so to start with a good sling, 30 with a crappy one.
For unarmed, I'd say around... 50? Not exactly sure, as I haven't punched a fox to death in a while.
No idea regarding melee, sorry.
I like my coffee like I like my bunnies. On my feet. Don't ask.
also depends what moves you have and the fox's level. I started hunting foxes around 40 melee and didn't have too much trouble. You'll figure out what moves/skills work for you the best. Dataslycer has a nice combat guide in his sig or you can look here: viewtopic.php?f=2&t=6518
"Love is what separates us from animals " "No, Lister. What separates us from animals is that we don't use our tongues to clean our own genitals. "
My first fox kill was 10MM and a Q15 sling. It took a good 3-4 minutes and alot of rocks. It's not efficient by any means (at that low of MM, anyways.) Took a long time to charge the sling, too.
I'd recommend what these guys are saying here, - about 20-30 MM and if you can pick up a Q20+ sling all the better.