60 days in Sumatra.

I am planning a trip to Sumatra, Indonesia around june-August next year, ideally to do across the island. Priority is the nature, volcano/mountain hikes, forest.. one option to fly to Medan and make my way to Jakarta(fly out) or start in Jakarta and make my way to Banda Aceh. But from there how to get to Malaysia or Thailand? Is there any ferries? Any good interesting spots to visit there, Lake Toba will be priority. I already been to in Java (did some travel in jakarta, bandung, and surrounding places, surabaya,ijen volcano, and ofc bali, so no interest to go there. Any experience? Any interesting places to visit there? Plan to land with e-visa for 30 days and after extend for 30 more days Thank you