Nouns: meaning and clear style

Separate explained answers

1. Two servings or cups. The count use is natural in an ordering context; coffee can also be uncountable when it means a substance.
2. Has. The number is singular. Contrast A number of complaints have arrived, where a number of means several.
3. We discussed the problem. A direct verb makes the everyday sentence clearer. The original formal wording can be grammatical but is heavy for a simple email.

Use your own accurate wording when explaining the reason.

Review the two rules

Meaning determines countability. Coffee is usually a substance, but two coffees can mean two servings.

Find the head noun when choosing a verb. A noun such as approval can name an action, but a direct verb is often clearer in an everyday email.