An SSD works in the same way as a regular HDD in terms of what Windows sees, a drive for storing data. But SSDs are more expensive per gb of storage so for a large collection it is more economical to use a HDD.
The external drive is a good idea, providing the virus/malware doesn't attack external drives as soon as you connect them.
I also read that SSDs can lose their data if they are left without power for a long time. I don't know whether that is a problem with modern ones and it rarely happens as people use them all the time and keep them powered up so it doesn't make them as good for archiving info.