Looks like you want to add the benefits of an Invisibility Sphere to your Tiny Hut.
4th level might be a bit on the low side - after all, you are combining two third level spells. 4th level is also where you get the Secure Shelter. Nice secure cabin, but obviously not invisible.
6th level gives us the Magnificent Mansion - Rope Trick on steroids. Your spell isn't that powerful.
So, I'm thinking 5th would be a reasonable sweet spot for your idea. I think to make it worth a 5th level slot, I'd remove the condition that the caster must remain inside the hut/hemisphere. Giving it a bit more flexibility.
The only remaining thing I can think of is how to deal with attacks originating from inside this buffed up Invisibility Sphere. You don't want attacks to 'dispel' the field, nor do you want to have it act like a group Improved Invis. So, perhaps - attacks originating from inside the sphere flip it from Invisibility to Opaque, essentially blowing the "invis" benefit.