Sastan is a great spirit to work with if you want to learn how to see spirits. There is nothing sinister about him (in my experience) and he does not usually make a grand entrance. He always just kinda “popped” into existence with out making any fuss. If you have the mastering evocation course then you will be doing some work with him, if not then make sure you have a scrying mirror, fire, or bowl of water with you when you call him.
Good luck and get ready to see the Snake Man!