Benvenut Flora!

It's simple - Roth wanted as much power et al as he could muster.

He wanted to kill Frankie to hurt the Corleones since the Rosatos would then take over more of Frankie's territory.

I find no evidence that Mike suspected anything about Fredo prior to the nightclub.

"Generosity. That was my first mistake."
"Experience must be our only guide; reason may mislead us."
"Instagram is Twitter for people who can't read."