I agree with Vargras, you should do LotSB and Arrival after the suicide mission. That's the way Bioware intended it.
And yeah, the main story of ME2 is really short if you don't consider the recruitment/loyalty missions part of the main story. Even though they are to some extent optional, though, I consider anything in the "missions" tab of the journal to be main-story, and anything in the "assignments" tab to be a side-quest. Especially since the recruitment/loyalty missions can have such a huge effect on the final main story mission.
*Edit* - Also, what dialog is odd if you do Overlord after the suicide mission? I've always done it after the suicide mission and I've never noticed anything strange. (Answer in spoiler tags, please.)