Just my 5 cents worth, buy all the components from the one place. Either a local store or repair vendor. Reason, if something goes wrong then they will sort it for you.
My Son and his mate were after a pc they were going to build themselves, and had used price spy to ID all the components from all over the place. I convinced them that although it may be cheaper that should something go wrong, 1, your are buying the components from everywhere, 2 you are assembling the pc yourselves, 3 if something goes wrong then all the places you purchased from are going to blame you the other place/part etc etc. Essentially you wont have a leg to stand on CGA wise.
PS: I used to operate my own pc repair/support business.