Yes, they are. The graphic novels do a good job of introducing new fans to the Buffy universe. They have all the elements that made the TV show popular, like the strong characters, the fight against vampires and demons, and the drama. Even if you haven't watched the show, you can easily get into the stories.
I'm not sure specifically as there could be various themes. They might continue the story of Buffy and her fight against supernatural forces, perhaps introducing new villains or exploring more of the characters' backstories.
I don't have definite information. But sometimes characters come back in new comic series based on fan demand or to further the story. So there's a chance Spike could show up, but nothing's guaranteed.
In some episodes, Buffy has to perform certain magical rituals. There was one time when she was in a trance - like state while doing a magic spell to close a portal to another dimension. Her focused and intense look during that time was very appealing. And the way the magic energy flowed around her made the scene quite sexy in a sense.
I don't think you can simply say the comics are better. The TV series has its unique appeal in terms of visual and audio experiences, while the comics might have more freedom in storytelling. It all comes down to what you value more.
The presence or absence of souls for the new vampires in Buffy comics is not straightforward. It can change depending on the plot and the intentions of the creators. Sometimes it's used as a plot twist or to add complexity to the characters.