Appreciate the input.
Still considering going the do-it-myself route, but lately time is pretty tight so I'm weighing all my options.
Number of SATA slots should be listed on motherboard description. PC description may list MOBO model. Cheap HP/Comaq etc PCs most likely have crappy PSY, which may not have enough connectors to power as many HDs as you want to add. I build last 4 PCs i had and i remember maintaining/upgrading my parents HP was royal PITA. If going with retail PC, have they configure it for you.