Well, imagine your editor lugging around five unbound manuscripts, bumping into someone, and dropping them. Without the appropriate header information on every page, putting those five manuscripts back together would be a nightmare. This time I haven't dropped down more than a couple of lines from the header, just far enough so the header is nicely separated from the manuscript's text. All pages of the manuscript also have good-sized left and right margins. There's a reason for this.
Margins are the perfect place for editors to jot down notes and corrections.
Right and left margins should not be less than one inch wide. I still use Courier 10 pitch font, which is pretty much standard. You don't need fancy fonts, and you definitely don't need any colored fonts. Your font should always be a nice, dark black. Editors and agents do a lot of reading, eye-strain is a very real job hazard.