Hi there,
You can theoretically setup the hard drives in raid 1+0 but this would nullify any performance gains made by putting the two 1TB hard drives in RAID-0 because it would be constrained by the slightly slower writes to the 2TB mirror drive. I recommend using a software utility that performs an automatic backup to the 2TB drive every 24 hours or so while you're sleeping. It's not necessary to backup everything, just the stuff that you want to keep.
As to what you should expect will depend on how it's setup.
On an AHCI controller such as the Intel I/O Controller Hub featured on all 900,3,4,5,6,7 series motherboards the two or more member drives will be exposed individually for SMART monitoring purposes but the storage area will be exposed as a single logical volume to the operating system. Thus, volume level operations such as de-fragmentation will span all appropriate disks but disk level operations will impact only the specified device. This is the best of both worlds and works very well.
On discrete RAID controller cards such as those available from 3Ware, EMC, Promise, Dell and HP the operation may differ. Many of these are may operate using different command sets or even translate command sets. As such, monitoring and exposure methodologies may differ.
Performance wise RAID-0 offers diminishing returns. Adding a second disk increases synthetic I/O measurements by about 85-100% which is very good. On real, IO heavy applications this translates to a performance increase of about 33%-50%. On applications that are not heavily dependent on hard drive I/O the performance gain is about 4%-5%