To me I would be bringing up to 35 players to the March camp. And that is without some of the stupid suggestions on some podcasts.
Simply put this is an opportunity to check players against players - whether they get game time or not. Is it Behich, Elder or Farrell to be coupled with Bos? inter camp training where Farrell gets under Irankunda's skin are essential to teach Irankunda not to respond. Every other country will know how emotional he gets. Popovic needs to get in his head that hard challenges are part of the game and reacting is exactly what the other teams wants. i.e. they are distracting you from your game and hoping to get you sent off.
Bringing in Volpato and Arena into a camp should be about familiarising with the set up and the rest of the squad. If they want to make a commitment then they can be picked (if warranted) for the World Cup or the Asian Cup.
TBH the only older player I would consider after the the World Cup would be Ryan. That means no Behich, Duke, Goodwin, Irvine, Burgess, Izzo. There are six players that immediately need to be replaced for the next cycle. If Ryan gets passed by 3 keepers he doesn't go to the 2030 World Cup. If he is still in the top 3 he goes as the veteran backup. TBH I am yet to see someone operating as well or better - and they are operating at a lower level.
There are problem 15-16 players that you can assume will be on the plane. Getting people in to train with and against each other in March will be as important as the games themselves