Miranda and Jacob are the only required members (you can choose not to re-activate Legion), since you need to recruit only three members to trigger Horizon (Zaeed counts as one), and six total crewmembers to trigger the Collector Ship mission (and, again, Zaeed counts toward this total). This means that three out of eleven crewmembers are totally optional. Other than Miranda and Jacob, you are free to choose who you want if you don't want to spend the time for a full crew.
On a side note, I have discovered that it is entirely possible to get level 30 on a single playthrough; you just need the Long Service Medal for the 25% experience bonus. Having a level 50 or 60 character does not matter, since I used my imported level 49 character. I obtained level 30 after the Reaper IFF mission. All you need to do is just complete every side-quest available (barring a few, since I missed Conrad during my ME1 Renedage playthrough), and you'll get it after the Reaper IFF's 1250 exp gain.
EDIT: I don't know why, but it brings me much amusement to hear Tricia Helfer/Caprica Six/EDI say "Really, Commander?" and "Probing Uranus."
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