where I should stay at for my visit to Panda Center in Chendu?

Stay at the city center. The panda center is in suburbs and it is not convenient to see other sttractions of the city if you stay around there. Weather not bad in June and July, just a bit hot. Yes, Xiamen is far away from Chengdu. As to hotels, I suggest Corown Plaza Chengdu Hotel or Prime Hotel - Ginza. They are close to the bus stop of 902 which runs to the panda center directly.

Hi there,
The Chengdu Giant Panda is a little far away from the central Chengdu and you can not find an appropriate hotel to live nearby. I still suggest you may live in the downtown. The Buddha Zen Hotel which is next to the Wenshu Monastery or Tibet Hotel which is on the 1st Ring Rd. is both great choices I think.
The weather in June and July is extremely hot in Chengdu. But sometimes the weather in Chengdu is not stable. You may check the weather forecast in advance.
Xiamen is quite far away form Chengdu, Sichuan Province.