Welcome from here, as well, jrp! Just a couple of obsevations:
Of course, the fatal flaw in the plan is that Tessio severely underestimates Michael's cunning and instinct.
I think it should be kept in mind that Vito guided this whole idea, though Michael eventually executed it.
I think that Clemenza's death would almost have to have been part of Barzini/Tessio's plan. Too much history with Vito, too much of an equal to Tessio to be trusted to let things stand.
Finally, as I've mentioned elsewhere, you can speculate that Tessio may have been in league with Barzini all along. This thing where he knows the restaurant and even the configuration of the toilet tanks is very fishy.
