I'll have more of a look at it, later, but one thing that stands out to me is the power supply. Your pc might not even start with a 300 watt power supply, and even if it does the power supply will be very inefficient at that capacity and won't last for long. Power supplies are most efficient at around 50% capacity, so try putting your build together on pcpartpicker, and then seeing how much power it requires. You will then want to try getting a power supply that has double the wattage your computer uses. Also make sure you get a good quality power supply; it is a very important component and will quite possibly take other parts of the system with it if it dies. Seasonic is a good brand, and most of their focus series of power supplies has 7-10 years warranty. Corsair also has some good power supplies, but don't get anything from the CX series.
If you tell me your budget, the country you are in and what games you will play on this computer, I can put something together for you on pcpartpicker. However, it might be worth waiting until next year if you can, as you have missed the Black Friday deals, and there will be new ryzen CPUs and AMD graphics cards in spring/summer.