You typically put your operating system and programs on the SSD, but you only need about 30GB for that. You can put anything else that's performance sensitive on there, image caches for example. I have a 120GB 840 pro SSD, 75GB used, 49GB free, but I have no swap file on that disk, and I have office, photoshop suite, development tools, etc, etc. You can put as many disks in your computer as you like, I have one SSD for OS and programs, another SSD for image cache and similar, a spinning disk for my personal data, a spinning disk for my commercial work, and a spinning disk for my media, so two SSD and three hard disks. When you have multiple disks you just make sure your data goes onto the large spinning disk, not the smaller SSD. Suggest 240GB or similar SSD is more than enough for most people, so long as they have a big disk for data.

Forget RAID, it's to ensure uptime for servers, it's rarely useful for home machines. An SSD is faster than ten RAID'D disks, in this context, seek time wins with OS and programs. RAID 0 SSDs makes little sense, RAID 1 for protection would make more sense, though backups are more than enough unless you can't tolerate a few hours or a day of downtime if the disk ever fails.