Which gear level do i need for the Legendary Events

for palpatine and cls I can say yes. But you do need decent mods on STH and Farmboy to get past tier 3 of cls events.
for r2 I don't know I used 2 G10s and 1 G9, and 2 G8s. Tried less than 10 times. So maybe all G8 will still do if you try on and on.
for Thrawn many people said they did it with all g8.