I don't think anyone has a great read on how the bench will shake out for Opening Day, including the Mets. The only lock right now is Juan Lagares, who is expected to start in center field against left-handed pitching. Other than that, because Ruben Tejada and Alejandro De Aza may still end up on another team, the other four bench spots remain up in the air...
The back-up catcher will be Kevin Plawecki or Johnny Monell... or maybe someone not in the organization yet. Terry Collins recently said the front office is debating whether Plawecki should be a back-up catcher for the Mets or go to Triple-A Las Vegas where he can play every day (either behind the plate or getting work at other positions).