ER, team and rot?

should I build ER on Varesa and if yes how much to aim for? I have 1 fav in team (c2 Iansan c1 Durina and Nicole she is on fav) and what is rot? I am guessing something like During EEQ Iansan EQ Nicole E and idk about Varesa what to do. Also I have c6 chev but idk if I should use c1 durin and c0 fav nicole or c6 chev and Mavu/c1 durin even though no hex buff