How can a peninsula have two "finished" ends. If you are talking an island, you need a more substantial look than just a "panel", so I would go with at least a 3" look. The middle photo is about right.

I like the thinner end panel in the middle pic, too. Not only is the apron more aesthetically pleasing, but it will add support, so you wouldn't need an integrated steel frame.

IMO those type of support panels always make the seating feel tight and there is no reason for them with the nice steel supports for overhangs. If you have a peninsula you will only have one end anyway .Maybe post a pic of the plan

You need 24” per stool, so the more space you take from that, the tighter it will be. Less than that and only small kids will be comfortable. Adding an end panel will make it feel tight too, no matter how narrow, because the person at the end can’t swing their legs out to the side to get in and out of the seat. I liked the panel look too but opted against it for that reason. Our peninsula is 61” with 2 stools

It looks as though it is about the same as the width of the electrical socket, so probably closer to 3" than 4".

You can do it either way. We have put the supports on both ends of a peninsula just to balance it out and create symmetry that the customer wanted. Obviously, one of them is only decorative and applied only on the underside of the overhang. They do use up some space. The peninsula we did was larger than yours - 3 stools for 8' peninsula. The ends take up about 5" if you want decorative panels.