Despite the increased tire width, if your overall tire diameter will be larger than what the JK sport comes with, you will need to reprogram the vehicle for the increased tire size, if your dealer swaps your stock wheels for Rubicon rims and tires before you drive off the lot, they should be the ones reprogramming your computer for you. If the vehicle you bought already comes with 32" tires and your just swapping for wider 32" ones, you won't have issue with speedometer and rev points.
With 285 tires you may be rubbing especially on the air dam as you fully turn your wheels so you may need to trim the air dam (very easy to do), or consider getting 1.25" wheel spacers (adapters) installed, they will give your vehicle a wider stance, probably look better, handle a little better and solve your rubbing issues, with the only downside being that you need to check their torque every so often, but this is easily done during tire rotations. They're a relatively cheap mod too.
If it were me, I would not be paying the dealer a $1000-$2000 premium for Rubicon wheels which is what they'll likely ask for. Even on our Canadian market, people are selling like-new Rubicon wheels with tires for about $1000-$1200, wheels alone can be had for about $400-$500. Plus you can sell your existing sport wheels and tires for at least a few hundred bucks.