Hyphenate only when used as a compound modifier.
She works part time. She has a part-time job.
Not PELL grants.
One word, always spelled out except in tables, business forms and statistical data or technical materials.
For percentages, always use figures unless the number begins a sentence. Use percent instead of the symbol, %, except in places where space is limited.
The College has a 4 percent increase in enrollment. She received a 90 percent on her test.
Periods should only be used with complete thoughts or sentences, and they belong inside quotation marks.