About the 4rth being summoned, during the Orichimaru vs. Sarutobi fight, im pretty sure Orichimaru was going to summon all three hokages but the third stopped the last box thingy from being summoned. Sarutobi literally thought "Thank god i stopped the last one". I think we can assume that the last box contained the 4rth and that Orichimaru can summon people from the stomach of the death god. But that still doesnt change anything inthe fight between Orichimaru and Itachi. I dont want to sound like a fanboy, but Itachi probably wouldnt even give orichimaru the chance to summon the fourth. Orichimaru even admit that he cant beat Itachi. end of discussion.

P.S. Does anybody know how many post counts it takes to become a genin? I thought it was 100.