I am planning to buy a Ryzen 5 3400g and the msi b450 tomahawk max motherboard with 2x8GB of Corsair vengeance LPX 3200MHz ram.
I have a 500W power supply so power should not be an issue.
I just went thru the same thing , building a "budget" PC. If you haven't bought any parts yet I'd maybe consider the 2000 line of Ryzen CPU's to save a few bucks, an AsRock B450M Pro4 and Ripjaws RAM would also shave off a few bucks and not make any noticeable dent in performance... But I don't know what your end goal for the build really is.
Anyway just came here mostly to say if you are getting a g series CPU why even bother with an older GPU with about the same performance? If your set on a discreet card ditch the built in graphics and get a few more cores & threads, or ditch the GPU and get more RAM.
I went with a R5 2600 and I also planned to buy a $100 used card to hold me over till I could upgrade. But did not really seen like the best idea since an RX570 wouild be like another 60. So I put an ad in the local buy n sell that I'm looking for GPU's and ended up getting a free Nvidia Quadro 4000. Yeah that card is old as balls and performance wise it's ranked bottom of the barrel, but it plays Skyrim on max and most of my other games I play are older or not that intensive on graphics I have not yet even had a need to upgrade except for gear lust.