Why did he have to shoot McCluskey and Sollozzo? When they found out they were eating at Louie’s they could have easily sent a hitman to be eating at another table and when Michael got up to go to the bathroom he gets up and shoots them. Michael comes out of the bathroom, everyone is freaking out having seen the hitman, and Michael just leaves and avoids having to go to Italy for a year. Plus avoid a possible problem with planting the gun if the gun happened to not fit behind the toilet. I always had a problem with that scenario.

Yes, I think it's something of a plot hole. All you can do is assume that they were so intent on backing up Michael that once the information they needed came in they just never reconsidered whether he really needed to be the one to pull trigger.

I think Solozzo would have been looking for a hit man in that restaurant--he probably had a sixth sense for that. The noveol says he had a man at another table in the restaurant. When Michael asked to go to the john, Sol looked toward the guy for an ok.

But, I agree that Michael didn't have to be the hit man. Michael told Sonny and Tom, after he volunteered to kill Sol and McCluskey, that the Corleones could get away with killing a police captain because he was "mixed up with murder and drugs...We have newspaper people on our payroll, Tom--they might like a story like that." Carry that a step farther: Tom could have leaked that story to the newspapers without Sol and Mac being killed. It would a major scandal that the papers would have given it such a big sendoff that the Commissioner would have had to suspend Mac, and put his own men to guard Vito. Sol would have been hunted down by police and be killed "trying to escape" before he'd be able to blab about his relationship with McCluskey. And, Michael could have gone on to college. And. we would have had no Godfather Trilogy.

Also, in the novel Michael says that he seems to be the only one who can get close enough to Sollozzo. Sonny states that Sollozzo has Michael down as faggy, so Sollozzo he won't be expecting danger from Michael. Tom asks the capos if they've got a real special hitman to do the job to which they reply "nobody that Sollozzo wouldn't know." Tom asks about somebody special who hasn't made his reputation yet. Tessio replies that that would be like bringing a guy up from the minors to pitch the World Series.

Turnbull, if Sol had a man at another table in the novel, what did that guy do when Michael came out of the bathroom shooting? Did Michael kill him also?

The guy shows Michael his hands are empty, and Michael walks out.

Sollozzo would have never expected Mike to attempt a move.
1) Mike wasn't at the meeting with Vito and Sol.
2) Mike had no track record of being in the Family business.
I don't care what Mike told Tom and Sonny,it was absolutely personal.
Had Mike not arrived at the hospital when he did,Vito would have been dead. In Mike's mind, McCluskey was a scumbag outsider who sold out to Sol.
For what it's worth,at least with Sollozzo, it was part of this "Sicilian thing".
And as we all know,Mike had to kill McCluskey because "he injured me",first by setting up Vito,then by breaking Mike's jaw in public.
Christ,Mike killed his own brother for no reason other than Fredo being a doofus who got played by "that Jew in Miami"
As far as the whole restaurant set-up,well "the Corleones played this one beautiful"