It depends on how you're using it.
If by 'staff' you mean a group of people (office staff), it is already plural and doesn't need an s after it. Possessive form would be staff's.
If by 'staff' you mean a stick (I'm going to whack you over the head with my staff), then the plural would be staffs. In this case, the singular possessive would be staff's and the plural possessive would be staffs'.
No, the noun 'staff' is a common noun, a general word for a group of people who work for a company or an organization; a general word for a group of officers assisting the officer in command; a general word for a pole, stick, or rod used as a support for walking or as a sign of authority; a general word for a flagpole; a general word for the five parallel lines used to write musical notes; a word for any staff of any kind.
A proper noun is the name or title of a specific person, place, or thing; for example:
The word 'staff' is also a verb: staff, staffs, staffing, staffed.
Staff is a common noun. Unless at the start of a sentence (as here) or as part of a name or title, it should remain uncapitalised.
not normally unless it is someones name
do you capitalize the word protestant
No, you do not capitalize the word drama.
Capitalize the word architect only when it is part of a title.Example:Senior Architect, Joe Smith
You do not capitalize the word quarterback unless it is at the beginning of a sentence.
No, but you capitalize the name of a biome.
No. It's not necessary.
do you capitalize the word protestant
No they shouldn't be capitalized.
It is not necessary to capitalize the word "yo".
No, you do not capitalize the word drama.
Yes, you must capitalize the first word, UNLESS it is a small word, such as "It" or "A" or "The".
Unless "it's" is the first word, there is no need to capitalize.
No, you do not capitalize the second word in the complimentary closing.
You would never capitalize a word because of the comma. Onlt capitalize it if it's a word that is always capitalized like France, I, Tuesday or Frederick.
Only capitalize 'spelling' if it is the first word in a sentence.
do you capitalize every word in veterans day ceremony
Capitalize the word architect only when it is part of a title.Example:Senior Architect, Joe Smith