My solution, start in normal mode and type:
Note that the first '<,'> will automatically be inserted on the command line when you press the ":" key after typing "
vip" in normal mode.
The first substitute joins the paragraph into one line, then the "|" character delimits a second :-command within the same command line, and this time the "
'<,'>" must be typed by hand. The second substitute command replaces a period, question mark, or exclamation mark followed by a space with the matching symbol and a newline.
This won't catch instances where a sentence ends with a period/excalmation/question and a quote character, etc. but the pattern can be extended to do so.