RAID 10 was suggested as "the best" for performance *and* redundancy. 6 seems fine, and honestly, my 5 is probably fine for my stuff anyway.
as for the free drives, what does "free" mean? it shows up as "unconfigured" and not a part of anything. in that state, i can't expand my existing array (though i do have the option to "expand").
i'll play with it some more tonight and post any new findings.