Based on the requirements i made a quick schematic and board in Eagle available here. The size of the circle depends on the chest size a lot. Imagine hulk wearing the arc reactor (LOL).
So, i used an A4 and drew circles of various sizes 5cm , 6cm ,7cm and 8cm. I then used a tape to stick them on my tshirt and see if it looked fine.
I went with the 70mm dia one.
It looked cool.
There were a lot of space on the board left. So, i wrote stuff on it. Made the open source h/w logo. Since, the project is open source.
Make and spread the Iron Man-ism :)