1. The whole fruit thing is not an accident. See the other posting on this page about oranges.
2. From another perspective, you could also draw a parallel between Zasa's killing and the killing of Bruno Tattaglia. Both hits were ordered by those assuming power while the current Don was hospitalized and unable to make the call. Additionally, both hits were ones that neither Michael nor Vito respectively would have ordered. The key difference here is that Sonny ordered the hit on Tattaglia while Vincent did the deed himself, presumable because it was personal between him and Zasa. And of course it is hillarious when Vincent looks at him after the shooting and says "Zasa" in a funny way.
3. The common tie between the murders of Fanucci and Zasa is indeed being murdered during the festa in the nieghborhood. Unfortunately, I think this was a result of FFC borrowing old ideas for GFIII.