A .22lr will do just fine for fox at short ranges (50yrds or so). Ultimately, it all depends on your ability with the rifle. If you can put 5 shots onto a 50cent piece at 100yrds, then you can kill a fox with a .22lr at 100. Use 1.5-2" as your guidepost for determining your maximum range.
I'm not aware of any state that allows hunting with field points, and frankly, it's a bad idea. A small dia 2 blade will slice through a fox, leaving you with a very simple stitch job.
Personally, given your location, I'd be looking at a 20ga with 4 buckshot. Much better choice for fox, and surprisingly nice on hides compared to its stopping power.