The Mull and Iona Transport Guide has just been published. You can look at it here. It gives you information about the ferries to Mull, which bus services go where, where you can charge your electric car, how to hire a car if you should need to, how to arrange a taxi and even where to hire an electric bike.
It is possible to get to Treshnish by bus now – right to the road end. The Ulva Ferry Community Bus runs a scheduled service on a pre booked basis conveniently on a Friday and a Saturday so you can use the bus to connect Treshnish with Salen where you can pick up the Tobermory to Craignure bus service to and from the ferry.