It shouldn't bottleneck it, as long as it can reach the Max Boost Clock of 4GHz.
Just ensure it doesn't overheat to get the most out of it.
Note: For CPU-intensive games, you can always lower some settings a bit, but from what I see, you probably won't need to...
If you mean this one: https://pcpartpicker.com/product/TnhKHx/asrock-z390-taichi-atx-lga1151-motherboard-z390-taichi yes, it is a fairly decent motherboard. Just make sure to update its BIOS, because some of the reviews I found report better performance upon the update.
PcPartPicker has a large list from which to choose: https://pcpartpicker.com/products/motherboard/#s=30&sort=-color&Y=600062,600082 (I've also added Black/Silver, deselect it if you want).
Note: Here is a filtered list with the best motherboards out there(Z390 chipset)...
To be honest, I've never heard of Fantech or Plextone before, so if I were you I would either get the Razer Electra or the one of the Redragon headsets.
But make sure to collect more opinions and check out reviews before you decide.
Yes. Even though it may be a bit bottlenecked by your CPU, it has a mere 75W TDP(I think it doesn't need a power connector, it is powered only from the PCIe slot), making it perfect for the limitations of this PSU.
Well, this is an office computer, so anything that could stress that PSU should be avoided.
I would recommend swapping the PSU, but if you don't want to, you are limited to cards with low power draw(gtx1050,gt730, gt1030,hd 7750).
In any case, you may want to reapply your thermal paste, or get a new cooler.
Thing is, even the stock cooler should be fine... are you sure it is mounted correctly on the mobo?