Cool. The Titans were only disempowered, not gone unless they were imprisoned in Tartarus for offenses against Zeus and his divine order. Prometheus, for instance, was a very important culture deity who was said to deliver a variety of useful technologies to humanity, in addition to the fancier stories about the gift of fire and the instructions for how to gift meat to the gods while still having a nice feast for humanity without offending Zeus by giving him the crummier portion. There was nothing at all unsavory about asking him, or, say Rhea, the Titan queen of childbirth, from attending to your problems alongside the Olympians who might be bothered to show up (they were probably too busy receiving awesome sacrifices somewhere, though). Titans and Olympians who didn't have a beef with each other cooperated on shared domains, but also sometimes competed over them. Zeus procreated with many Titans.

Now appealing to Hecate could be a bit unsavory because she was an underworld goddess not contained within Zeus' pantheon the way Persephone was, but she was also seen as an earthly household deity. Her cult was widespread, often worshipped as an aspect of Artemis (earth)/Selene (sky)/Hecate (underworld). There is no single, definitive version because the very international Hellenistic culture of the Mediterranean of the second half of the 1st millennium BCE had a lot of different local traditions that are incompletely and unevenly preserved. Depending on the region where you wanted to focus, you might have totally different stories representing probably their own ritual practices loosely affiliated with other Hecate cults by Panhellenic stories.

Sorry I can't muster more than that. I'm pretty tired.

I'm sure there are some texts on knowledge about intentional practices, like herbaria, and maybe more esoteric practices, but I don't know those off the top of my head.