If you arrive at Chengdu in the morning, I think two days are enough. Half day to see the Sitting Buddha, then head for the mouontain and leave the second afternoon.
You can take a train to Chengdu, then change to a bus at Chengdu Tourist Transportation center (xinnanmen Coach station),成都旅游客运中心（新南门汽车站） to Leshan. It will take you directly to the sitting Budda attraction site. It operates 7:10-19:35 every 20 minutes.
There are many hotels around the mountain. It is not allowed to camp on the mountain, but still there are people doing it. But for safety reasons, better not do it. There is a camp base at its foot.
Emeishan is a natural resort, not need to hire a guide foe me. If it is a place of historical relics, then a guide will be needed. you make the decision.

Thank you, Mr Cai, this is very helpful information. I will try to do this without a tour company