Help with new bike
You'll find the 4.0" tyres are amongst the smallest fatbike tyres you can get. You may find 3.8"
I went the other way & out 4.6" Specialized Ground Controls on mine. You will find slick/semi slick fatty tyres, that's maybe what you should be looking at.
If you're on Facebook there's a bike group you can join, plenty of ideas & inspiration on there.