DS journey should be done with DS characters imo. To me it doesn't make sense that all those light side characters come and work together only to turn Anakin into Vader/ or even make existing Vader stronger
It should be like a dark version of Yoda's training, or DS going against Jedi/Republic to make more sense. Just my 2 cents.
Requirementa could be
Sid, Dooku, Grievous, Maul, Nute
for a new Vader(Pathway to darkside sort of HJ class event)
or
Palp, Stormtrooper, Veers, Vader, Snowtrooper for Vader's unique as you suggested(Sith training sort of legendary class event)
