Creating an array using your existing SSD will destroy all the data on the drive. Your best bet would be to create an image of your existing SSD, then after the array is created restore it using software like Macrium Reflect, TeraByte Image, Acronis, etc.

RAID always starts from ZERO, so backup all data first. You thinking of going RAID1? (I don't see the need...). The new SSDs, specially the Crucial MX100 are beginning to be made with all sorts of safety mechanisms to never lose files to the aging SSD

The Evo is still better performance than the MX100, but the security measures on the MX100 are levels of magnitude better than the Evo. The Evo should last less as well... 3-bits per cell instead of 2-bits per cell (MX100) will cause extra SSD writting per cell. Unless you are copying 50GB of info everyday for 3 years straight, either SSD should last at least 7-10 years (way enough)

In terms of SSD life time vs HDD life time, it depends how you use it. If you bang it against the table the SSD lives another day, while the HDD dies. If you copy and delete terabytes of info on a daily basis, the HDD will last longer. With the new SSD tech, chances are you'll buy a new laptop before the SSD begins to degrade. Think... when was the last time you bought a new flash drive? or a new memory stick for your camera?
For cloning, I like Macrium Reflect... nevertheless, I've always had issues when cloning back. I think the best method is to save files and then do clean install if really needed. If you have RAID0 both SSDs will be formated and turned into RAID0. If you clone RAID0 to external HDD, it'll copy everything as if it was 1 partition. RAID0 is "technically" 1 partition with the size of both SSDs. The computer just tosses info left and right to each SSD. If one SSD becomes corrupt (happens on HDDs as well), then if the file has pieces on both sides, you just lost it. RAID0 is for speed, not reliability.
If you clone back from HDD to RAID0 SSDs, the info will be tossed into both left and right.

Don't buy a Crucial MX100 to put it in RAID 0 with the EVO, what happens when you mix diff. drives for RAID is the speed will drop down to the lowest drive so get another evo with the exact same size for your RAID 0

RAID aside, the EVO still performs better than the Crucial MX100. Although it's a great SSD for the money, for pure performance, the Samsung 850 PRO, 840 PRO, EVO, along with the SanDisk Extreme II are among the highest performing drives out there

I have 2 SAMSUNG 840 PROs 512 GB and one Samsung 840 EVO 1TB mSATA drive. why didn't I choose RAID 0? I tried it, even though the sequential read/write speed is double that of a single drive, the most important test score which are the 4K random reads and writes where a user will really feel the difference at the OS level were actually 10% lower on the RAID 0 setup. With that said, for sheer speed, I choose to go on a single SSD setup and store my software installation EXEs on the 2nd drive and put my videos, mp3s, etc on the 3rd drive which is the large 840 EVO 1TB mSATA