https://pcpartpicker.com/list/B6VNgw
Example only.
Here's what I would do in general:
1) build system
2) MEMTEST86 prior to clean Windows install www.memtest86.com (run full pass)
3) reinstall Windows (be careful to not lose data/passwords)
4) allocate VRAM in BIOS (up to 2GB I believe). That would then leave 6GB approximately for Windows/games to use.
5) later if needed get:
a) an identical 2x4GB kit for 16GB total, and
b) a graphics card (i.e. GTX1050Ti or better)
*Note that the CPU portion is nearly identical to a 4C/8T R5-1400 which isn't too bad. Mine's barely better (i7-3770K @4.4GHz) and very few games have much bottleneck in terms of average FPS at 2560x1440 on my GTX1080 (most gains would be high FPS gaming at 1080p or avoiding certain stutter situations caused by CPU bottleneck).
Hope that helps somewhat.
*The R5-2400G costs about $20 more than the R5-1400. So you're paying roughly $20 for the graphics portion which is quite good actually. So unless the budget is quite a bit higher it doesn't make sense to go with a different CPU + dedicated graphics card.
The R3-1200 CPU is only 4C/4T (no hyperthreading) so even though it's $60 cheaper than the R5-2400G it doesn't make much sense since it's a weaker CPU plus you need a graphics card anyway. You probably know this but it's worth mentioning.
**So I agree an R5-2400G is a great APU provided you know how to build and potentially plan for an upgrade.