also i am thinking of making a background with a brahmin or 2
this is actually a good idea :)
also i was interested to help and typed in "sketching a mouth" at google picture search.
and you wouldnt belive, i found awesome stuff, check this:
(http://vilppustore.com/vilppublog/wp-content/uploads/2011/07/Drawing-the-mouth-4.jpg)
(http://www.graphicmania.net/wp-content/uploads/Mouth_Collection_II_by_anathema_creature.jpg)
lovely mouthes. choose one of them and keep on minimalism.
and here another good link for your style, a nice minimalism artist named phil gibson painted this acrylic/oil painting, the picture is named "sunset drifter"
(http://img0-ec.etsystatic.com/il_fullxfull.276428612.jpg)
but hey, you don´t even need a mouth. check this:
(http://4.bp.blogspot.com/-Xsbm_uCFPxs/TyKwH7RupII/AAAAAAAAS5Q/254ylENuwFw/s1600/Frederic_Remington_-_Arizona_cow-boy.png)
just add a mustache!