Raid can increase performance and can add some data protection, but comes at a cost. Raid 0 is just adding 2 drives and striping across them increasing speed, but if 1 drive fails, you lose all data on both drives. Raid 2 is mirroring across 2 drives and provides data protection in case 1 drive fails, but does not increase speed. Raid 5 uses 3 or more drives to stripe across, and provides data protection against a failed drive and increases speed. Raid does not replace the need for a good backup strategy. Most of the restores I do are because of corrupt data, or because someone deleted something. Rarely do I restore a whole drive because of a failed drive. If it was me I would just get 1 large SSD.
Depends. RAID configurations always have the ability to fail. If you want to use RAID 1 I say more power to redundancy. If you want even more insane speeds, RAID 0 is the way to go. This is mostly personal preference. 1 drive is in some ways 'safer', but as we all should know stuff breaks for no reason other than to make our lives miserable at times. Personally I have two 60GB SSD's in a RAID 0 as my MBR, and two 1TB HDDs in a RAID 1 as storage (for redundancy). I dont save any files to the SSD other than the OS/Installs so if it does fail, or a drive does go bad, I don't loose any information. My speeds are well into the 180% range of a single SSD, and I love it. Worse case is that I have to re-install windows...which would absolutely crush my spirits...or not . I also changed the registry to put all user folders on the HDD. I could honestly not care less if the RAID 0 fails. It may be a small pain, but I believe the rewards are greater than the small risk.
Edit: If your only storage is the SSD or 2 x SSD in a RAID 0 I would only use one SSD drive, but realistically I doubt you do not have a HDD to act as storage.
Its literally as easy as changing '%SystemDrive%\users' to 'D:\users' There are other ways to do this but making this registry change is really that simple. The SSD drive tells you how to move folders without changing the registry. But there are issues I noticed when doing it that way. The Move User Folder shows you how to change the registry, and then tells you to make a new account. It is a bit more advanced, but the worse thing that can happen is that you have to re-install windows.
That wasn't rude, that was telling someone that they need to do some research on their own. Raid setup and configuration is a massive task and tough to take up here. People seem to not want to do their own work anymore and just have someone hand them the information on a silver platter.
Typically a larger SSD is faster than smaller SSDs (1vs1).
RAIDing a pair of SSDs will disable the Trim command (a form of garbage collection), which will cause the SSD to slow over time and eventually require a secure erase (basically resetting every byte in the SSD).
An SSD is extremely fast in general because of it's lack of seek time. Raiding them may improve throughput but you likely won't notice it very much over a single SSD.
Personally, I'd go for a 120GB these days, but 240GB are getting to the point where it's a dang good deal too. I have a 60GB myself and find that it's more than enough for me with my users and program data folders relocated to another drive, and using mklink to move games to the SSD.
If you are a gamer, look up SteamMover, it will let you move individual steam games off your SSD as well. I usually install steam to the SSD, mklink the steamapps folder to an HDD, then use steamMover/mklink to move indivual games to the SSD.