I take foxes with a .204 Howa 1500 and wouldn't change it unless I won the lottery (at which point I'd buy a stainless Tikka in .204 instead, and that's only because I'm yet to see Sako do a .204)
32 grain V-max bullets do all you need to do and more on Charlie if you put them where it matters. A LOT of foxes could vouch for that fact since I got the rifle a few years back.
I don't change mag or turrets on the scope as I prefer to leave well alone and learn adjustments using mil-dots. A 100yd zero means I'm aiming high by 0.2 mil dots at 200 and 0.6 mil dots at 300yds. 500 yds is only a 2 dot lift. With a 1/2 mil dot reticule the adjustments are easy to judge and very few foxes inside 400yds ever hear the bang
Yep, the .223 is legal for small deer and .204 is not, but the OP asked about a foxing rifle and that's the question I'm answering.
If the OP is ever up my way (Northants) he'd be welcome to come and put a bit of lead down the tube and see for himself.
As for lamps, I was using a red Tracer scope mounted lamp, but have recently changed to a scope mounted Sniper Hog with a red pill and it's an amazingly good beam of light. Now using the Tracer as a hand-held spotter.