Either way, a single space should follow every comma, semicolon, and colon. In the UK and other parts of the Commonwealth, the practice is the reverse. Underline text if you cannot italicize it. Long passages with underlines or italics are hard for the editor to read and will be just as hard for your other readers. Don't use a right-justified margin .
Most word processors can kick such paragraphs onto the next page.
This may create huge lower margins, but it's usually better than breaking a paragraph. Be sure that each page displays a plain arabic numeral in the upper right-hand corner. Otherwise, don't bother with a header. It just wastes ink. If you must make manual corrections to your final printed ms., make them as legible as you can.