I read this page and it helped me get to know gumpaste a bit better. I too am a just experimenting with gumpaste so I wish I had more answers for you but I don't.
http://offthelist.wordpress.com/2010/06/09/te/
Keep everything because sometimes things we would never think to be a write off are. I had no clue for a long time that my parking slips because I have to pay for parking near my shop were a writeoff (not huge) but every cent counts....
I use poured fondant. very easy to decorate with when in a food safe squeeze bottle.After I am done with it I put it in the fridge and take it out and use again and again.I have so many colours made up and ready to go in my fridge at...
I usually start with 2 drops and add after that to taste. Everyone has a different taste. I have gone overboard with oils in the beginning of my experience with them and let me just say I learned my lesson well lol