1, 2. "Pasta" could be considered either a 4th declension noun or a foreign word, in either case the genitive is the same as the nominative. Theoretically the plural would be "pastaí" but I think it's safe to say that it doesn't exist in real life (even in Italian the plural form of "pasta" is never used). 3, 4. There are two different nouns with the form "sú" in Irish; one is masculine and means "juice", it has the plural "súnna"; the other is feminine and means "a kind of berry" and it has the plural "sútha"; so the plural of "sú talún" is "sútha talún". Since "sú" (both meanings) is in the 4th declension it doesn't change in the genitive: "lots of strawberry" = "go leor sú talún"; "lots of strawberries" = "go leor sútha talún". 5. This is the other "sú"; your examples are correct, and together they would be "súnna" = "juices".