There are no firm rules on overhangs. Yes, the perimeter and island can be different. That 1/4" won't even be noticeable. Usually you want to make sure the overhang extends beyond your hardware so you aren't leaning against knobs.

If the side of the cabinets are visible (like from the next room), then yes, I'd do it the same as the fronts. The overhang on either side of the range opening is usually just a small 1/4" lip or so.

I'm probably doing 27" deep counters, so ~3" overhang on the perimeter so I have countertop in the corner for the appliance garage (fridge is on other wall), and because my range is 36.5" deep. But my island will be approx. 1-1.5" overhang.

Thanks, Natschultz. Good point about taking the knobs into consideration. I may do 1" on all the counters. Still haven't decided and the fabricator will be here today!