To visit Emeishan, I want to know the weather there.

Since you plan to Lugu Lake and Mt Emei, I advise you to visit the mountain first and then the Lugu Lake. You can take the train from to Xichang from Emei city. There is only one coach from Xichang to Lugu Lake at 08:00. The ticket price is 75 RMB and will cost you about 7 hours to reach Lugu Lake Town where you can take local mini bus to reach the Lugu Lake.
As for the weather, it is cool and you need to take some thin sleeved clothes. It is the best time to see the red leaves on the mountain.

But I'm coming from Lijiang, stopping in Lugu Lake and heading east to Emeishan and the rest of Sichuan, so I want to know where and at what time I can get a bus from Lugu Lake (Lugu Lake town, Luoshui, Zuosuo?) to Xichang.

If so, you can ask the owner where you live. There is no bus station in Lugu Lake Town, so you can ask the owner of the hotel you live in. One of my friend did so when they went to Lugu Lake.
The bus from Lugu Lake to Xichang leaves around 08:00 in the mornings. The exact time of the depature time, you still need to ask the owner of the hotel for help.
From Xichang to Mt Emei, you need to take the trains.
I hope it is clear enough for you.