These days, building an Intel-powered system doesn't make sense for most people unless they are buying one of the more expensive CPUs. For everyone else, an AMD Ryzen system has a better dollar to performance ratio.
As such, I would recommend you a B450 motherboard with a Ryzen 3400G CPU. Ryzen CPUs need fast RAM to function well, so make sure you pair it with (2) sticks of 8 GB RAM that is rated to run at 3200 MHz. Slower RAM will slow down the CPU, as will buying only one stick of RAM (you should have 16 GB of RAM total).
The integrated graphics in this CPU actually function quite well; you should buy these parts, try them all together, and if you like your gaming performance, you're done. If you want more gaming performance, you'll then need a more powerful and higher quality PSU to pair with the RX 580.