In this context, “equipped creatures you control” and “equipped creature you control” refer to any creatures you control with Equipment attached to them. In the highly unusual case that Stone Haven Outfitter becomes an Equipment, the meaning of its abilities doesn’t change. The bonuses continue to refer to any equipped creature you control. They aren’t bonuses applied solely to the creature Stone Haven Outfitter is attached to.
I am trying to determine whether the highlighted case is at all possible. I know that I can turn non-Creature, non-Equipment Artifacts into Equipments with Bludgeon Brawl, and that I can turn non-Artifact permanents into Artifacts with cards like Mycosynth Lattice. So, for that highlighted case to be relevant, the only requirement is for Stone Haven Outfitters to become a non-Creature permanent. Is there any way to do that with currently existing cards?
Alternatively, is there any way for a non-Creature permanent to gain Stone Haven Outfitter's abilities?