There is no point in having a RAID0 setup with a NAS device.
Ethernet is roughly 10.5MBytes/second and wi-fi is usually around 3MBytes/second but wi-fi varies by signal strength.
USB2 is limited to no more than 32MBytes/second (not the USB2 limit; it's the SATA->USB converter chip limit).
The only scenario it makes sense to RAID0 an external drive unit is if it is frequently hooked up via SATA or USB3.
Actually, there is another scenario and that's when file size drop very low. Find a benchmark such as HDTUNE for a hard drive and look at file size read vs access speed. If you are transferring very small files on a regular basis and dropping well below 10MBytes/second for a single drive then RAID0 on Ethernet would improve things.
**Keep in mind RAID0 will significantly increase the risk of data loss. A single drive failure loses all data.