yes
Yes, you should capitalize the first letter after a comma in a sentence.
Capitalize family titles when they are used as names. For example, "Where are you going, Dad?" Do nott capitalize family titles when they come after a possessive noun or pronoun or an article. For example, My sister teaches at the university.
Capitalize only the first letter of the first word of your phrases of salutation and conclusion. i.e. My dear Josephine, Very truly yours,
In the salutation "Good day to you," you only need to capitalize the first word, "Good."
Only if it is the first word in a sentence.
"Who sells it?" is correct (always capitalize the first letter of a sentence).
No, you do not capitalize "first birthday" in a sentence.
yes
At the begaining of a sentence, and the first letter of someone's name.
if you mean from the beginning of a sentence yes then you would have to anyway because its at the beginning of the sentence anyway.always capitalize the first word of a quotation if needed.
You do not capitalize chickenpox in a sentence. The exception is if the word is the first in the sentence.
You should capitalize the first letter of the sentence "Who is your favorite French artist?"