Andy,
You have the pro's help here, but maybe I can add something. You can make a component from one-half of our model, copy and scale by -1 and have symmetrical parts. Then you only work on one half, the other side will update accordingly.
To see some basics on fabric shapes, see Daniel Tal's video here:
http://sites.google.com/site/3dbasecamp2008/all-sessions-2008/working-with-terrain-and-other-irregular-surfaces
towards the end. Oldie but goodie. Then going to Curviloft and Extrude by Rails & other plugins you can expand on your organic modelling abilities.
Peter