I just returned from a weekend at Lugu lake. It's a bit of a pain to get there because they're fixing the roads, so you need to switch from the big bus to a small bus for the small mountain roads, and then back to a big bus. The whole trip takes around 8 hours—if there are no traffic jams. That said, the scenery is beautiful! The bus from Lijiang costs 100RMB. There are two buses per day at 8:30am and 9am. Once you get to Lugu Lake, there's a 100RMB entrance fee that lets you go anywhere and stay as long as you want.

Unfortunately, I don't know anything about how to continue from Lugu Lake into Sichuan, since I just went back to Lijiang after circling the lake by bicycle. But I hope this is helpful!