You don't need a centrefire to shoot a fox on the end of your barrel, (even though some here don't feel capable), after all they are only about the same size as a medium size dog, and if you can't stop that with a 30g V-Max at 322 ft lb then you need to take up knitting not buy a centrefire! You will be in CF territory if you want long foxes, as per my post at #2. Commonly the .222, .223 and 22-250 are quoted, the .243 with a light V-Max eclipses all of them though.
Scope and mod will be down to the rifle/calibre you buy and your finances and personal preferences!
So what'er you s