Itinerary feedback

Sounds like a good plan to me.
I didn’t know that had the snowmobile activity on the glacier in the summer months.
Are you planning on see the whole golden circle or on so the snowmobiling ?
With our family, it took the whole day to explore the golden circle.
Have a great adventure!

This looks like a fine plan!
On the golden circle I highly recommend lunch at Fridheimar, a greenhouse farm where they grow tomatoes hydroponically. They have converted one of their greenhouses into a fantastic restaurant that offers all you can eatdelicious tomato soup and homemade bread. It's a very unique place...reservations necessary.
Your itinerary is good...just make sure to get an early start since there is a lot to see in between the sights you mention...Diamond Beach, the beach at Vik, several waterfalls, and lots of horses!

I think you are making good use of your time as far as destinations go, but I would caution you to not do too many activities. You seem to have 4 full days and have 5 activities planned. We were there in September for 7 days, and had 4 activities, one of which was cancelled because of weather (whale watching.) We often felt we were constrained by time. Most activities want you to get there a half hour ahead--get outfitted with crampons for glacier hike, flotation suit for boat trip, find lunch somewhere. So a 3 hour activity became at least 3 1/2 hours. We enjoyed the ones we did, but were happy on the days when we had none planned so we could see the sights at our own pace and be open to the unexpected things we saw. The company that helped us plan recommended no more than 1 activity a day. Take a look at your activities and see how much time the company says you need then add finding the place, parking, checking in, getting equipment, to their time estimate. I know they all sound interesting, but you don't want to be ruled by them.
Have fun, Iceland is awesome