Like the title says, I'm thinking about returning to ESO, now should I start a new toon or pick up where i left off, (somewhere around morrowwind area)?
Do whatever is fun. My suggestion would be to do both. Continue with your familiar toon and create some new ones.
Try the new Necro class if you haven’t yet and check out the vampire changes. Plenty of new content to see and new dungeons have been added, some with unique mechanics. Enjoy