Router multi part inlaying

Sorry to post this here but I can't seem to find a Router Forum and my idea will be used on my wood turnings.
I'm intent of making my OWN inlay multi part router system for bowl crack repair.
I have the basic idea but what I need to produce is a positioning piece into which any number of templates can fit.
In this way I could use a different template to cut out the different coloured parts of the inlay.
I am a long time woodworker and have done extensive work with plastics which I would like to make the parts from.
My problem is that I think the positioning piece would have to have a rebate around the edge into which the pattern parts would fit tightly. My issue is how to make the 'hole in the positioning piece.
I do have some ideas about using a square piece of hardboard and a router template guide to cut the hole but am not sure how to make the rebate.
I don't have access to CNC and this is a small job that I think might be overly expensive to have made.
I do know this Forum has a lot of very smart artists and craftspeople and I would really appreciate all ideas and input.

Can't you use the router to make the rebate, once you have the hole cut? Use a bit with a bearing guide to follow the hole (the bit obviously has to cut a larger diameter than the bearing)... Or is there something I am missing in what you want to do?

Not sure I understand what you are describing but how about having somebody make it on a 3D printer? There are several services that can connect you to printers in your area.

Thanks guys. The issue for me timothy is that I will be working with 1/4" thick lexan and most rabbit bits I know have a space between the cutter and the bearing which I think will give me problems. Sorry if I didn't explain the project better.
Mark that's an idea I'll check my area for printers, do you know if these printers can print clear material? I will be best if I can see clearly through the material while I'm cutting the inlays.

Pete, Here is a link to the service I used to use:

https://www.3dhubs.com/3d-printing/#3dp-processes

Clear printing info:

https://all3dp.com/2/transparent-3d-...sparent-parts/

The downside to this is somebody needs to design the part in a 3D modeling program. I did all mine but some printers will do it for you if you send them a sketch.

Just noticed that Staples does 3D printing:

https://3dprint.com/96380/staples-sculpteo-launched/

Also, what do you mean by a “rebate”?

Do you have any pics of the templates?

Thanks Mark. I'll see if this will work. I appreciate you taking time to try to help me. Hopefully I will be able to make it work and post a few photos here if I do.