I like the idea of using Julia B as a receiving opposite too!
About the MBs, I would take Lara to the main team. Julia K and Lorena good prospects and I believe in their potential, but I'm not sure if they're ready. I understand that going to the Olympics would be a valuable experience for them and I can see them being very important for the NT in the future, but, at the end of the day, there are only 3 spots. Let's say one of Carol or Diana (assuming she'll be the starter) gets injured or is having an off day in an Olympic semi-final, who would you rather have on the bench? For me, it's 100% Lara.