1)is there a russian corrispective for the italian name "Leonardo"? (which is my name)
Hmm. Леонард…Леонард Иванов sounds a tad surreal though))

Значение имени Леонард, что означает имя Леонард


2)is it possible to create a Russian diminuitive/nickname from my name (both affectionate or rather formal)
Леонардик, Леонардушка, Леонардушек, Леонардусик, All of these names are informal, diminutive and affectionate. Леонардушка is my best choice (it’s almoslt like Иванушка)). A bit more formal shortened name that can be coined is Лёня.