need your approval

I have been having a tough time to figure out when I should or shouldn't put an "a" before the words like breakfast, lunch, and dinner. The below is the explanation that I came up with. I would appreciate to hear your thoughts on it.

I think the sentences below are all correct.

1. Have lunch.
2. Have a nice lunch.
3. I eat lunch at noon every day.
4. I have a lunch to go to today.
5. Let’s invite them to dinner tomorrow.
6. I hosted a dinner for twelve last week.

What caused my confusion was the ambiguity of these words. I couldn't understand what, for example, "dinner" exactly means, but I finally realized it contains two aspects, "food (in the evening)" and "an event (over dinner)."

When the former aspect is emphasized they are uncountable, and when the latter is emphasized they are countable, I figure.

So:
"lunch" or "dinner" in the sentence 1, 3, or 5 mainly refers to the food aspect.

"lunch" in the sentence 2 basically means the same as the one in the 1. It is used as a uncountable nouns because of the existence of the adjective.

"a lunch" or "a dinner" in the sentence 4 or 6 mainly refers to the event aspect.

Thanks for your tips.
M