Could Italy have remained a more or less democracy?
If not a Fascist state how much does it change.
If the King call Benny bluff at Rome and arrest him with all the other fascist leader, basically destroying the PFI there is still the socialist (plus the fascist remnants); a period of political violence will follow, with a crackdown of the socialist with an authoritarian goverment with the direct imput of the king at least for a while.
After that a period of normalization will come, with probably the same series of brief and weak goverment like the French.
Any difference to Hitler?
Well anti-semitism will be a non issue, expecially of the nazi type as a so important place of the race on the ideology programm
Is it decisive in preventing the Right winning the Spanish Civil War?
Without all the aid that Benny give to Franco, there is a lot of chance that the Republicans will win...after that (more brief civil war) probably another will arise between anarchist, the communist and the other if the friend of Stalin don't purge/eliminate the other factions before the end of the war. This can make Stalin more adventurous, as the Republican failure made him very skeptical on aid foreign communist/left party on take power.