As an Android Developer I've worked on different projects where hardware was part of the product.
During most of these projects the idea is simple, the first sample is quite doable and the sales might come easy.
But then you have to actually build something that can be taken into production and meet all the regulations. This is where your garage solder party ends and the big problems may arise. I'm happy to inform about how to make a real product instead of a unsellable sample.