I believe I'm in the second act since there are now a bunch of sidequests after having cleared everything on my list. My next priority mission is to go have a chat with the Quarians. If I was to get the DLC, it would be because I want to add story and context about the Protheans. I am hesitant to get it because it sounds like I would only get that context if I take the Prothean with me on missions. Would it be worth it to get the DLC now or is it too late?

@golguin: Buy it, but keep the guy with you for the main story missions. He has really interesting input on the Prothean's fighting the Reapers. If you do not care, don't buy it. Also, at your point, bring him on the next immediate story mission. You can thank me later. :)

@golguin: probably should have got it earlier, but ya you should be fine. Get it now so you can have him in everything else from now on.

@BlatantNinja23:

So bring him to every main story mission? What about the sidequest missions? Liara has become a permanent member in my party with her bubble stasis so this would basically lock my party to Liara and Prothean.

If you want the ending to make more sense, yes.