I have more faith in the psu that shipped with the dell than a raidmax.
All the parts on the list will fit in the case you have.(apart from the case) the power supply and the motherboard header is the only issues I can see.
for an interim upgrade the GPU would show benefit almost immediately.
you already have mass storage 640GB hdd, an ssd as the boot device would yield more benefits immediately.
the motherboard RAM and CPU will have to be installed as a block, all together. al the other parts can be added at a piecemeal basis.