Your problem occurs because of partition division. it can also be because it only has 1 hdd or ssd. if in a laptop installed 2 storage or more problems will not occur again this happened because of the installation of the os and storage in 1 hardware.
that's a good choice, you want the series r7 2700 or r7 2700x
both of them are capable.
just install a VGA card with a minimum price of 150 $ like RX 570 or better bcause R7 2700/x not have APU
enough,
You can use the PSU calculator at https://www.msi.com/calculator
from the hardware you use it uses 600w of power
but consider if you add other hardware such as a fan and others then I recommend using a PSU at least at 800w
hy.. you can use easus data partition, it can fix all your problem moving or migrate your os into new hardware ( new HDD or SSd) with all your hardware installation and acticvation ..