I have finished testing assembled modules. Only thing left is to connect them together and mount then in enclosure. I am planning to finish hardware part of the project this weekend. Here is picture of Led matrix PCB running test software.
Here are also some pictures of the enclosure. I have tested few types of adapters and straps (apple watch compatible off eBay) and they all fit perfectly and snugly. Magnets work and fit great although they might be tiny bit too strong.