Just an update here, in case it helps anyone. Using only the 3400G CPU is not adequate at all for anything in VR. I tried it, and while you can get in to VR, you are getting about 2 FPS. It's just not made for it and it will NOT be fun. It's for desktop gaming only, not VR.
I am still using the 3400G as my CPU, but I have since purchased a 2070 RTX graphics card. Now this setup is very adequate for many games, videos, etc, and the 3400G allowed me to build a PC initially without a graphics card and then add the card later, so that was a nice touch.
However, using a frames per second application within VR video apps, I see that some videos are actually CPU-bound on this processor (meaning the CPU is chugging away at 99% capacity while there is still ample capacity on the graphics card), and these videos are stuttering.
For the above reason, I am looking to upgrade the CPU to one of the new 5000 series. I am just not sure yet which is adequate for the need, depending on what can be found: the 5600x, 5800x, or 5900x. But I am hoping one of them will fix what stuttering remains in some videos and games currently being CPU bound.