Yes, you are rather right. We usually use ‘lunch’ without any article when we mean it as the normal food we eat. However, when we want to qualify it, we may say: I had a sumptuous lunch today. The lunch was very delicious.
You could say that without an adjective preceding the word ‘lunch’ but you would have to indicate that this lunch was a particular one and would need to define it as in -
We had a lunch together to celebrate his recent exam results. We always have lunch at this restaurant on her birthday.
Then, “let’s break for an early lunch at 11.” is also the lunch is particular one because it will happen early… Because of the adjective “early” specifies “lunch” here, then an article seem needed here. Am I right? Please let me know!
That’s right. You can specify the noun luch with adjectives such as an early lunch, a great lunch, a lazy lunch, etc. Since these describe specific meals you need the article ‘a’ or ‘an’.