As others have said, the grammar is fine, but they're not very smooth & natural expressions, they're a bit awkward, especially the first one. Consider these alternatives: I'm happy this week. I'm very happy this week. I'm so happy this week. I feel happy this week. This week I'm happy. This week I'm feeling happy. This week I feel happy. I'm happy so far this week. I'm happy with my week so far. I'm having a good week. I feel happy. I'm having a good week so far, so I'm happy right now.

These sentences are almost correct but could sound more natural with slight adjustments: "My week is happy." This sounds unusual, as "happy" typically describes a person rather than a week. You might say: "I'm having a happy week." or "My week has been good/happy." "My favorite food is sandwiches." Grammatically, this is correct, but to match "sandwiches" as a plural noun, it’s more natural to say: "My favorite foods are sandwiches." or "Sandwiches are my favorite food."

Both are fine. You don't need to speak with scientific precision. Everyone knows the meaning of a happy week.

Both expressions could be improved for natural English. Here’s why: "My week is happy." In English, we don’t usually describe a week as "happy." A more natural way to say this would be, "I'm having a happy week" or "This week has been great." These alternatives express that you feel happy about the week. "My favorite food is sandwiches." This sentence is almost correct, but "sandwiches" are plural. It sounds more natural to say, "My favorite food is a sandwich" (if you mean one type in general) or "My favorite foods are sandwiches" (if you like many kinds of sandwiches). Let me know if you'd like more examples!

I’m having a happy week. My week has been happy so far. More likely to say “great” than “happy” .