Hi,
1) Yes, not only is 4GB not enough, but you also need two sticks (preferably 3200MHz) setup in Dual Channel or the Ryzen CPU will be running too slow (depends a lot on the program/game too).
2x4GB 3200MHz DDR4 Corsair...
for example. (some kits, especially cheaper, lesser-known companies don't always work as well). It's best to find a kit and use the EXACT same model for your MOTHERBOARD (exact model) at 3200MHz if it's 3200MHz memory kit.
2666MHz is the minimum (again 2x4GB) but aim for 3200MHz unless the cost jump is too high.
2) overclocking is silicon lottery mainly. as said, look online. VOLTAGE affects heat (temperature, i.e. 75degC max load sustained) so you should monitor both stability and temperature when experimenting.
3) do NOT overclock until the system has been running at least a week without issues.
4) run MEMTEST86 on the system memory (DDR4) prior to installing Windows www.memtest86.com
- it's not critical it be running at the max speed on building. You can leave at default speeds if you want, but if you overclock (or let motherboard setting run at max profile of say 3200MHz) later you need to RETEST with Memtest86 again to ensure it's stable.
5) BIOS update:
That's the first thing I'd do..
a) BIOS update (need another PC)
b) optional: optimize DDR4 profile
c) Memtest86
d) Install Windows + drivers
e) test a week
f) OC CPU, check temperature, optimize fan profile (motherboard support site for software)
etc