Sure Mike, although I don't think I can save you any time.
The more you work with Graphics the more time you put into them, to make them the best you can. It pulls you in.
I use Photoshop 6, it's an older version but the extent to which I use it (as complex and multilayered as my Decal images are they are made with basic moves in PS and I have only scratched the surface in the 9 years I have been using it) PhotoShop 4 or 5 would suffice.
Creating images that get printed out no larger than a 1" square or at the most 2" x 1" is slightly different than designing something as large as page size Art.
One has to be mindful of how an image will appear, and what possible aspects of a design would not be visible, at such a small size.
As for Decal Paper I've tried them all and for some time, years, I have only used Decal Paper from Papilio.com
All my work is done using Clear Glossy InkJet Decal Paper.
As for sharing, sure, I've created and given away files online to let others Customize their DieCast with my Graphics that they can print out.
What casting are you working with?
I began by using Word to compose my Decal sheets but it is nowhere near as useful as a copy of PhotoShop.
I wrote a "Make Your Own Decals Using Microsoft Word " Tutorial back around 2004 for a couple of dozen (at that time) Diecast Customizing sites.
It's very elementary, one of the first Internet Tutorials I posted, but until I put up my "Decals In PhotoShop" Tutorial it may break the ice for you and give you a feel for things.
I'll find it and post it in the Tutorials section.
I thought when I came here there would be lots of dialogue concerning Graphics and AirBrushing for such a large Model site so it's good to see some.