I have this kitchen right now. What I tell people? The only thing I would change is I'd want a prep sink. My island is only 5 feet so I don't think it's big enough for one, but yours is. if you keep it, though, I'd consider off centering it so you get a nice big prep space to one side.
If you don't prep on your island though, it wouldn't be useful.

It's 13 feet from the front of the refrigerator to the sink and the island is in the path.

Yes to prep sink. Move it closer to the fridge but leave a landing area for things coming out of the fridge.

I have a similar layout and I use my prep sink *all* the time. I use it more than my main sink, actually. I second the off-setting recommendation, placing it closer to the fridge.

Bringing the prep sink closer to the fridge with a landing area makes a lot of sense. I’ll talk that over with our kitchen designer. Our cabinets aren’t hand built custom cabinets so we are somewhat limited to what we can do.

also consider putting your trash closer to your main clean up sink (switch the mixer and trash).

I think a prep sink in your kitchen layout is definitely the way to go. You have the space . And it allows for both prep and clean up at one time. A true " two person" kitchen.

Show your husband the yellow lines compared to the green lines:

I have a large kitchen 16x20 with a large island. I do not have a prep sink, don't want a prep sink and have never missed a prep sink. I honestly think it comes down to personal preference.

My kitchen (mid-remodel) is very similar, and our prep sink is not installed yet.. my husband, who wanted little to do with the design of the kitchen and doesn't really cook, commented just the other day on how nice it will be to finally have a sink in the island. Even aside from how many steps it will save (so many!), I will be so thrilled to separate the vegetable-cleaning area form the dish-cleaning area. He cleans while I cook, and we are so often in each other's way with one sink.

I also added a prep sink to my new kitchen...cabinets are in, counters next week. I can walk around now and "pretend to be using both sinks" and it was absolutely the correct thing for us. Family of 6, someone is always lining up to use the main sink for something. No more! Wide aisles and 2 sinks was the starting point for my design.

Thank you all so much. You have been so incredibly helpful. We will be switching the trash and mixer location. Possible even removing the mixer stand. (Interested in your thoughts on that too.) We are going with the prep sink. I hope we can move it over slightly towards the fridge without making the cabinets awkward.

I have a smaller kitchen and admittedly small island. But I went with a prep sink anyway and am glad I did. It is closer to the end of the island that is nearer the refrigerator and I do use it all the time while prepping fruit, vegetables etc (the sink also has a garbage disposal). Its location gives me additional room for meal prep as well as space for others using the main sink to work at without us tripping over each other. Trash cabinet is at the end nearer the main sink. Very happy I went with the prep sink.

Did you put a garbage disposal in your big sick as well. What size prep sink did you go with?

IMO I wouldn't waste a cabinet on my mixer but I don't bake much so I don't mind hauling it out of the pantry when I do. I can see it being helpful if you bake a lot, or if you have physical challenges lifting it. I don't fall into either of those categories so I would keep the cupboard space for more frequently used items.

Yes, my big (main) sink has a garbage disposal as well!

I actually envisioned using the mixer stand for my instant pot but I’m going to element it. I don’t think it would be as useful as I was thinking.

totally agree. and instant pots aren't that heavy. :)
I've read 18" min is a good prep sink size.