Need guidance on Shivanga Sadhana initiation (in description)

Hello, I am planning to do the Shivanga Sadhana (the one guided by Sadhguru) and I want to initiate without the Sadhana kit since there is not enough time left to order anything, so I have the following questions: 1. Vibhuti - can I get vibhuti from any temple, or any Shiva temple? I heard it’s not recommended to accept Vibhuti from anyone in temples due to the risk of occult practices, therefore need guidance on where to get Vibhuti. 2. Black cloth to tie around arm - recommended size of the black cloth is 18x3 inches. Is there a specific reason behind this or is it just because this size fits well for everyone? Can we use any black thread instead? 3. Rudraksha mala - will any single bead rudraksha or mala work (from any shop)?