Should there be a space after “No.”, “p. (=page)” before numbers and after “a./p.” before “m.”

Question

Should there be a space

• after “No.”, “p. (=page)” before numbers

• and after “a./p.” before “m.”

Answer 1

MLA and APA, although not explicitly outlined anywhere I can find, use a space after "p."/"pp.".

"No." also is followed by a space (see the aforelinked MLA page and here for an example in APA).

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There is never any space in "a.m." or "p.m.", but some style guides say to not use periods either, or to use small caps (please see the source; small caps don't work well here):

The Associated Press Stylebook:
4 p.m.

Microsoft Manual of Style:
4 P.M. (However, Microsoft prefers 24-hour time notations, in which 4 P.M. is 16:00.)

The Chicago Manual of Style
4 p.m. (recommended)
Also 4 PM or 4 P.M. (with PM in small capitals)

Garner's Modern English Usage:
4 p.m. or 4 PM (with PM in small capitals)

The Gregg Reference Manual:
4 p.m. or 4 P.M. (with PM in small capitals)

_{A.M., P.M., a.m., p.m.: What Is the Correct Time?}