Hello!!
Welcome to Airbnb. My first advice would be to deactivate instant booking until you get the feel of how hosting and receiving guests is like. Also, make sure guests can only book for the following 3 months and not have your listing completely open
Additional people should have an additional fee, you never know how many people will be shoved into your place.
Are you close by?
It's a big house, I wouldn't recommend just 1 night bookings as I am sure cleaning and adjusting between each guest will take most of the money earned from the first night.
The place looks fantastic! If I'm ever in Iceland I would seriously consider it.
Oh, I would put a bit more photos of the house and what's included and maybe a little less of the area (but do not take them all down).
Cheers!