Dear Pat,
Hang in there, you are on the right track by following the wonderful suggestions given. I used to grid and this has helped me to look strictly at the puzzle shapes that make up the whole. After I was shown how to use the proportional divider, I found that it is a faster and easier way to get the correct placement.
If you search you should be able to find one under $100 dollars. Here is one link
http://www.cgedwards.com/Weems/weems01.html
I now print the desired image in black and white, so I can see the value relationships, then I do a rough sketch, pick one reference point and start measuring. Since the former grid would get painted over, this tool allows you to double check yourself at any stage of the painting. The monitor is now used to zoom in to see details and for color reference.