Actually, you should use a period inside parentheses if the enclosed material is meant to stand alone as a sentence.
By the way, there is no space before the exclaimation mark in American English.
As for double spacing after a sentence, I had broken myself of the habit once I learned all publications use single spaces, but the iPhone has conditioned me to use double spaces again since that's the shortcut to drop a period at the end of a sentence.
Exactly, when I'm at a computer I sometimes find myself back in my old habit of double spacing, and that's because of the double space tap on the iPhone. Perhaps I should disable the double tap space and get back in the habit of sliding my finger from [123] to the period key to end sentences (which automatically returns to the alphabet keyboard). Certainly it would save me from having to press delete after the double space to end a paragraph.
By the way, there is no space before the exclaimation mark in American English.
As for double spacing after a sentence, I had broken myself of the habit once I learned all publications use single spaces, but the iPhone has conditioned me to use double spaces again since that's the shortcut to drop a period at the end of a sentence.