Make small test batches before you try large batches. Make it with fresh oil before you try waste oil. Start and finish the process in one session. Wear proper protective gloves, apron, and eye protection and do not inhale any vapors. Methanol can cause blindness and death, and you don't even have to drink it, it's absorbed through the skin.
Sodium hydroxide can cause severe burns and death.
Together these two chemicals form sodium methoxide. This is an extremely caustic chemical. Always have a hose running when working with them. The workspace must be thoroughly ventilated. No children or pets allowed.