DQ III Remake Opinions on my classes

So, as I head into end game I just wanted some opinions on where I should go, class wise, if I am interested in beating all the post game content. I turned my Thief into MA even though I think it may have been a mistake. I want to keep that one and level it up. I turned my Priest into Sage and will likely turn them into a thief once I get the last spell. My last character is a MW and now that I have wild side I was wondering if it is worth it to do Sage, then Thief on another character?

So I have

Hero
Thief-MA
MW
Priest-Sage and plan to move into Thief, soon.

Does having multiple thieves get you more items? Would it be very helpful to have another sage if I'm doing all post game content, or should I just save the time and turn my MW into a Thief?