Ryzen build

[xSMOK1Ex]

I am building a pc and have bought a load of parts already I have a ryzen3 3200g to go into a Asrock b450m Pro I have 16gb of 3200mhz ram a ssd 500gb and a 500w power supply for now I am currently looking for a graphics card the pc is for my son at Christmas and I am a gamer but my pc building knowledge is zero my son has picked the parts and says they should be fine but don't want him to have nothing to do after we have put it together and it possibly dose not work, I have since looked on pc part picker and it says might not be compatible parts the cpu and motherboard so like I say am panicking a little for him, all the vids on youtube of this same build do not mention any conflicts in hardware and are basically showing it fine so don't know where I stand any help would be much appreciated thanks

 

[xSMOK1Ex]

So I won't be able to just put the ryzen 3 3200g straight in and play then looks like I have made a big mistake then I only got that one for the integrated graphics for now a graphics card will be bought later down the line

 

[xSMOK1Ex]

And not sure on our budget for the gpu