Great place to visit. Can not help with a guide as I did a 1 week self-guided/driven trip many years ago - May was a good time. Also can not offer any accommodation tips as we wild camped & lived out of the car.
But places to visit for birds should include: Latrabjarg - for auks, gulls, etc. & Lake Myvatn/Laxa River - for ducks & phalarope -amongst many others. I'm sure someone will be along with the details you want.
We did a complete circuit of the island & the photo opportunities in terms of landscape, waterfalls, etc., are nearly endless - if you get the weather; apparently it has been a poor summer this year.
Bird list was 65 for the week.
Have a good trip.
Can't see the birds for the trees!