Forming negatives with "plus" (and a bonus question)

Dans l'écriture et le discours informel, est-ce que on doit utiliser ne avec plus pour rendre le négatif ? Par exemple:

1. Je ne veux plus de beurre. I don't want more butter.
2. Je veux plus de beurre. I want more butter.

Is it possible that given the right context one's speaking partner would understand (2) to mean I don't want more butter? Or must one always use ne in such an ambiguous situation? Are there more such examples of this?

Bonus question: In typing this up, I realized I don't know how to modify multiple nouns with the same adjective, particularly when they're of different genders:

1. l'écriture et le discours informel
2. l'écriture et le discours informels

Is either one of these correct, or neither?

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Edit: Je crois que j'ai trouvé les solutions des deux questions.

1. On prononce le négatif et le positif différemment, non?
2. Voici ci-dessous, de ce site web :

The case of nouns joined by et is generally the easiest. In this case, the adjective is generally always pluralised, provided that the adjective is genuinely intended to apply to both nouns.

If all conjoined nouns have the same gender, then the gender of the adjective follows that of the nouns (so above, blanches is feminine because both chemise and cravate are feminine). If their genders differ, then in careful writing at least, the noun is made masculine.