Certainly the USB host will be the largest task of those mentioned.

The USB device is also non-trivial but you can go from zero to hero in a few months on that end, especially if you have a framework to start from. One nice thing about USB is the built-in "flow-control" so that you don't have to buffer data or negate a clear to send signal. Generally speaking, the host will buffer data until the device takes it. And it will keep asking for data from the device until the device is ready to send it.

I haven't done ARM yet (only a matter of time), but your $5k per seat looks about right for typical tools.

GB