Pretty much correct. Though you don't need an SSD at all. If you really want your computer to boot in 7 seconds, instead of 27, it might be worth the money to you. =P But a 7200 rpm spinning drive will do you just fine too. Especially the Caviar Blacks. Along with Barracudas and Spinpoints, those 3 make up some of the best drives at the moment. More than capable of running everything you need them too.
As for RAID, as mentioned, it can be for backup, performance, or a mix of both. Really depends how you use it. RAID 0 is striped, which means it splits the info between 2 or more drives, so that it can load them faster, but if one drive goes, both drives have basically lost the info. RAID 1 is mirror, which is just as it says, an exact backup. This is good in case one of your drives goes down, so you still have the info you need, but at the cost of writing speeds, as it's essentially writing the data twice. RAID 5 is a good mix of both, you get the drive with the main info, striping to 2 or more other drives. Raid 10 [1+0], or 0+1 is both 1 and 0 together, so you can have 2 striped drives backing up into 2 other drives [which would be copies of striped drives], or 2 mirrored drived being striped to 2 other drives. This is one of the best for great backup [as you can lose any 2 drives and still have all your data], but also one of the most expensive setups. For gaming, I'd definitely say use an SSD main drive and 2 striped drives for data and the performance boost, but for audio, I'd probably go for a RAID 5 as best bet, but you need a 3 drive minimum, or just a basic RAID 1. Simple backup and only 2 drives needed, but a little performance loss when it comes to writing.