1. Good. Should have ordered it with a SSD, instead of the slow HDD.
2. No. Never use a raid0 for precious material like media or projects. The risk of losing all your data is too big a risk and it makes no sense to raid two SSD's on a USB3 port. Simply use a single Samsung Ti USB3 1 TB drive without trying to raid anything. That single and fast SSD will almost choke on the USB3 port anyway.
3. Use a Samsung T1 USB3 500GB drive for exports.
Use the existing HDD for backups only, possibly mounted in an external bay, connected over either eSATA or USB.