> It's easy to bridge from Arduino to Atmel AVR IF you know how to do board layout.
Design is half the battle: the other half is component selection and manufacturing. If you BOM is way off, you're SOL before you even start, and most people don't get this until it's too late.
This is why you don't design something around an esoteric part, like the only ARM part with 5 Quad SPI ports or a dual time base RTC. If you do, have contingencies for your contingencies, like merging footprints you can have the option to use different IMUs on the same PCB.
Design is half the battle: the other half is component selection and manufacturing. If you BOM is way off, you're SOL before you even start, and most people don't get this until it's too late.