Best Way To Configure Storage

Hi all, sorry for posting again, but I'm really having trouble deciding this..
My 4 WD reds just arrived, so I'm wanting to set it up tonight.

So far, I have the server built and running using a 128Gb SSD as the OS disk, so thats already done and WHS2011 installed and working fine.

I have a decent RAID card, so I have lots of options available. I was planning to use RAID 5, making my 4 2Tb drives into a single 6Tb volume, but I'm concerned about backing that up, as I know I can't make a backup larger than 2Tb.
So, questions. Can I back it up manually? Like just making copies of everything onto an external drive?

Should I use RAID 5, but partition it into 3 2Tb volumes?
Should I sacrafice more space and just make 2 seperate RAID 1 volumes of 2Tb each?

Is anyone here using a single large volume? And how do you back it up?

Thanks.