The wheels are difficult to know what will fit. Best bet is to find a wheel you like and call the manufacturer and ask them if they will fit on the 2019 Silverado. I can tell you that most Fuel wheel will fit but you will need to make sure you get an updated fuel wheel as they had to make changes to the wheels to fit over the calipers. XD has about 15 or so wheels that will fit. If you go to the manufacturer site and search for 2019 silverado, it will show you what will fit.
I am sure most manufacturers will tell you to stick with the 20x9 wheels, but 20x10's will fit, jsut depends on how big a tire you want and how much you want them to stick out. I wanted to put 20x10 -18, but they wouldnt fit with my 305/55R20 tires, but I do believe they will fit if you went with a 33x12.50 tire. So I have a 20x9 +1 wheel as I had already bought the tires and it was too late to exchange them. Also depends on how much trimming you are willing to do to the truck to get the tires you want to fit.