1) Seems like the best option for what you want. However as you've read up on raid options you've probably come to that conclusion yourself.
When you talk about data duplicity make sure that you get what you want. Raid'll only protect you against the failure of one drive. It is no backup solution
2) If you read around ths forum and others a bit this comes up quite a lot. While green hdd are good for specifically a NAS (the netwwork connection is the bottleneck there) it really depoends on the drive itself.
If you go for Raid5 purely for your pc you might see a minor speedboost going fron 5400 tp 7200 however don't expect anything spectacular