Hi Janet,
Ok, this is long posting.
I would start in the center with drawing a circle. You should be able to find something around the house that is the size circle you need to start with. I would make a paper template also.
Then use your favorite marking pencil or marker to draw the circle. You will then need a ruler and your marker. You can also use a compass tool to add your marker where the pencil normally goes and hopefully it will fit. You may have to visit your local artist's supply store or a drafter's supply store.
You can also do this next step just using a ruler. You will mark your desired space away from the center circle using the ruler and your marker. I think it helps to have the longest ruler you can find for this. You should try to keep one end of the ruler end at the center of the quilt. You can mark this spot with a small x-stitch and leave long ends to the thread. Then with the ruler just mark with dots the space away from the marked circle. After you move all around the circle making little dots, then connect the dots which will form your next circle. Continue out from the center circle until you have the entire quilt marked.
At this point I would try to hand the quilt so that you can review how the marked circles for stitching appears. At this point you can make any changes you think would be best before stitching. If you do find some changes you think you might want I might think about making them in a different color. The reason for the different color is that as you come to that section when stitching the color change will alert you to your change so that you can be a bit more careful as you stitch. You may want to stop and review your previous decision.
There is also another process that is not related to the stitch quilting process. Did you want input as to the design and pattern process of the quilt piecing? If doing this I would use paper. Draw your first circle, cut it out. You could even use different colored paper to make up your quilt pattern. (The colored paper would not necessarily be related to what the fabric colors would end up being.)
Then continue on making your circle templates. You could use freezer paper, wax paper, newspaper, typing paper, wrapping paper, brown paper bags, brown wrapping paper, tablecover paper, sewing pattern paper, etc. Whatever you feel you like to work with best. You may find using different papers will help aid in designing the quilt and making the templates. The different papers may add to seeing the design.
I would definately use a wall space to put your design on as you continue to come up with your quilt layout. With this process you could just continue to make circles in different sizes and they could then slip behind other paper layers on the wall. Once behind the center design you just pencil the line in on that paper piece. That will mark where a seam line would be as you work from the center area of the quilt out.
I hope that I've been able to explain what I'm thinking in my head. If not please pm me and I will attempt to explain further.
I think you have a great idea for a quilt. It could be quite striking especially with your fabric selections.
Good luck with your quilt and please keep us updated as you progress with your project.
Pam M