You have to follow the current recipes for legendary and journey events.
With the exception of gmy because of reasons, legendary toons require the opposing force to acquire. Journey toons require an early version of the hero with 4 supporting toons. So you can't have a hero journey for jedi Luke that uses Vader for instance. The logical toons needed for jedi Luke would be CLS, rolo, Chan, hoda and R2.
A first order journey for a new kylo is unlikely because we have the latest version of him already. We also lack 5 named first order toons. The issue with doing dark side journeys are that with the exception of anakins demise to the dark side, there are very few dark side journeys, and they all happen in clone wars and rebels. The two main candidates therefore and assaj (her journey from apprentice to bounty hunter) but then, her journey resulted from being abandoned by dooku. The other is maul. I know it comes up a lot but it really does make sense. His first fight would be alone against gqj, he would have a fight against savage (to see who was the master between them), then against sidious along with savage, one against GK and assaj together. Those fights all lead up to solo maul as the head of crimson dawn. They usually like a 5th fight in there so no sure which they'd pick