Depends on the gaming. If you go for simpler graphics strategy/ single player open world type games, an APU is fine, you don't need anything more than 60Hz, so Skyrim or Minecraft etc are decent. Even CSGO is simple enough, it'll run on a potato.
But if you prefer CoD, Battlefield series, even MS Flight Simulator, you need a gpu with some umph and a cpu that'll push the fps. And that's where the APU's fall short. Because half the space under the IHS is taken up with the graphics engine, the cpu has very little L3 cache and relies totally on the pc ram for any vram usage. Which is portioned out by Windows, so you end up with 2Gb of vram equitable at a slower speed, that's got to bounce back and forth through the motherboard, along with all other ram use, instead of a gpu direct connection.
APU's as standalone for simple stuff, the basics, are great. For anything advanced or complex, ehh not so much...
For comparison, the best Vega graphics are pretty much equitable to a GT1030 in performance and ability. And that's with a decent mobo and good ram. On the cpu side, the 10yr old FX-8350 with a decent OC and a Ryzen 3 2400G aren't much different.
And please don't do piece by piece. Don't get an APU and think to add a stronger gpu later, the cpu side of the APU still applies, whether or not the Vega graphics are used. Getting a stronger gpu will help with graphics details but won't do diddly for fps, you'll be stuck at snails pace. Decide on APU and call it quits, or keep saving and get a full ryzen/Intel with a gpu.