As far as I can remember, he was only prepping shigaraki to basically experience ego death by either being so obsessed with destruction that he resonates with AFO or killing his sense of self by revealing that his existence as a villain was by design, either way he takes over the body.
super regen was his crutch to physically hold all the quirk factors, so he never considered that the taken-over-body would be too weak.
His obsession with OFA was just him going "I own you" to his own brother I guess lmao
