Welcome!
The talking dog gives good advice. You are coming at a time when the worst pollution of the year is behind us, but we still occasionally have bad air days (which I consider to be when the AQI is over 200, which is when I wear a Respro mask bought at Natooke here in Chengdu). Natooke is a good place to visit if you need a mask, I believe they have a few different models for sale and they can talk you through the differences between them.
We also have a few articles published about protecting yourself from pollution like this one: How to Handle Chengdu’s Pollution Like a Pro
Enjoy Mike’s and Johnny’s, they are fine establishments. The produce market is also a great place to see local culture, try some new foods, and get ingredients for cheap.