your sash & ankle bands should be enough - i think the (RUSA) rule is just ot have reflectiveness on front & rear of you, and your ankles.
and yeah, it won't hurt to bring rain gear, but i might gamble it depending on what the forecast says.. a lot can happen over 600k!
so are you doing it straight through, or will you rest at the 400km point? i haven't decided which to do yet.