DAMN Rens!! \o/ Did you PAINT that photo-realistic beauty?? That's a lot of love that went in there! If you painted that hair, than that's CRAZY realistic! :O Awesome!!
My advice would be to make sure you have realistic expectations, and an efficient workflow-- before introducing UDIMs at all, let alone more UDIMs. UDIMs aren't a magic fix-all patch, you still need strong fundamentals or you'll end up working wastefully, and producing assets that are unnecessarily heavy. Just my two cents!