Vitz won't be able to cross Lowari Pass. Similarly it won't be able to do Ayun to Bamburet.
Your route would be..
Islamabad - M1 - Exit Rashkai Interchange - Mardan - Batkhela - Chakdara - Dir - Lowari Pass - Darosh - Branch left to Kalash Rd - Ayun - Bamburet (kalash).
Also take into notice that all accommodation in Kalash and Chitral have been prebooked by tour operators. So you might have trouble if looking to book for accommodation on the spot.