It's generally a bad idea to try to use trims for character modelling because it slows down interactivity.
From where youa re at now it sounds like to need to learn some multipatch modelling. There are a couple of tuorials on this site for modeling multipatch heads.
You will need to learn how to use the stitch,attach/detach surface and rebuild surface features.
The most difficult part of doing this kind of model is mainatining tangency across surfaces and you absolutely need to maintain the same number of isoparms across surfaces. A tip on how to do that is as follows.
Say you have to adjacent surfaces and the isoparms do not line up.
Select both of them and open the options for rebuild surface.
Your surfaces need to be uniform with the paramter range set to 0-#of spans. We are goign to make sure that they are uniform. Select reduce,0to#spansand Direction UandV,Global Tolerance and Nurbs Output.
One of those surfaces needs to be remade so that their isoparms line up. If both surfaces have isoparms that are unevenly spaced they both need to be remade the following way.
Set your component mask to line.
setComponentPickMask "Line" true; //MEL command
Now while holding the shift key select lines across the surface that needs to be rebuilt so that the new selected lines are lined up with the other surface.
Now duplicate surface curves..
duplicateCurve -ch 1 -rn 0 -local 0;//MEL command
Now with these curves still selected loft them into a new surface. Make sure that Uniform is selected in the Loft Options.
Now if you use the stitch tool and connect these two surfaces they should have pretty nice tangency.
If they don't then attach the surfaces using with the blend option then detach them and restitch.
This should give you some idea of what techniques you will need to acheive what you are after.
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