While a lot about Hearth has little rhyme or reason (besides "magic is weird"), the tip-toe thing does have something of an explanation. Fairies are sensitive to footsteps which they recognize by how much magic comes under foot with each step. Smaller feet are, magically speaking, quieter and less likely to draw attention.
His brain's functions are scattered since the expected organ isn't really there. His little people represent his conscious mind and most of his senses. His brain stem and autonomic functions are in the expected place in what space is left there. Everything else and particularly his memories are in the walls of the room in his chest.
Hearth's little people aren't visitors, they are parts of him. They don't normally eat and they drink tiny amounts. Their waste (what there is of it) is normally removed from their bodies by sweating. The larger body handles the major work of turning food into energy, the little people benefit from this without contributing.