I think Sasuke just doesn't wanna be disturbed while he's fighting Itachi and thats why gathering a group so they can take on any obstructions or intrusions coming in between the both Uchiha. Kinda like any Akatsuki member's intervening or something, although on second thought I think Akatsuki member's would be more than happy to let it happen just so only the ELITEST OF THE ELITE people survive in the Akatsuki, aka this being a test for Itachi and to see if he still "got it" to remain a member of the Akatsuki. The leader of Akatuki might even think of making Sasuke a member of Akatsuki once he has taken care of Itachi and "proven himself" worthy enough, etc, etc....
I think Sasuke might even end up joining Akatsuki after killing Itachi just to get a "goal" in his life or somethin in those lines![]()