There are several informative websites about RAID with linux. The one I've looked at most recently is here: http://linux-raid.osdl.org/index.php/Linux_Raid
. (mdadm is in the repos)
The answers to your questions depend on what type of array you want and the performance you need. If you're just looking for a remote, large space then JBOD may be an option vs. RAID0 or 1.
Having a separate drive for your OS and home would be my preference in that scenario.