He could do all the missions, just dont waste any time looking for minerals and artifacts on barren planets, waste of time for little credits and XP. Not to mention some of them are in the worst spots possible.
Yeah, even doing all of the side-quests, collecting most of the minerals/artifacts, and doing the DLC only took 20 hours for me. At the very least, make sure to do the Cerberus Missions and the missions that Wrex and Garrus give you after talking to them enough (and also do a multi-part Geth mission, as it gives you something that you need to give to Tali).
And for laughs, do the Conrad Verner side-quest too (which really only involves talking to him two/three times).