My 2 cents worth.
if it is just for office and you are building it for him, go for the H series motherboards. i3 processors should be sufficient. If want to save money, go for the older generation CPUs. 4th generation series. They still sell them in Sim Lim. Current generation is 6th going to 7th.
he is still schooling, got school work + want to game sometimes. Not sure how good is i3. To him, i think reliability is more important, but gaming cannot play dota2 also lag bah...
need os/peripherals? anything in his pc he could reuse?
From what i see, i think his mobo died. i am not sure of his current setup tho.
OS and Peripherals no need, just need the
CPU+
Mobo +
Graphic card (idk, but are all graphic card universal PCI-e slot?) +
HDD(not sure he want use old de or not) +
Disc drive(dunno old one compatible or not).