The hard drives and the ram are easy to install, when you get your Mac Pro the user guide actually tells you how to install both components. As you said it very easy to do, just remember to discharge yourself whenever you are touching components. Also take note with the ram installation there is a specific order to install them.
I would suggest get the ram from the macsales and for Hard drives, seagate, western digital SATA-2 drives from anywhere cheap in Australia. I grabbed a 1TB Seagate 32mb cache drive the other day for $180.
Also take note when replacing existing hard drives take it easy when pulling out the bays as they are quite snugg.😎