Agreed. The way I see it, the covenant cannot employ him full-time at this point, but as it develops further it might. You initially had plans for underground space, stairs, etc. So he could be a way to attain those. Furthermore
So the way I was envisioning it would be that he could work for the covenant to build the house, then move one for a few contracts elsewhere on the island (so he'd be a hook for some stories). Then come back to the covenant for more work, then a few more contracts. Then come back more permanently. So he'd become closer to the covenant as time goes by.
He can have some supernatural feature (virtues and/or flaws) but he should not be focused too much on the supernatural, I think. He'd need to be able to navigate mundane circles without too much trouble.
If you want to give it a spin, then go ahead and post the basics in the Character Concepts topic.