For my money, this is the most comprehensive tutorial covering this subject:
Learn how to make your own vectorportraits | Vectorportraits.com
It includes sections on skin shading, clothing and other details.
Of course, for "true" vector work, you should be using Illustrator, not Photoshop, but the above tutorial gives a very good overall result - as long as you're prepared to put in a reasonable amount of effort.
Oh - and as for being "afraid to close the project", don't forget
Ctrl+S is your friend. Hit it on a regular basis.