I'm a bit embarrassed by all of the "store bought modules", rather than having rolled it entirely on my own from bare chips. But they're so incredibly cheap to buy that way! Cheaper than the bare parts (by a long way). Eg. about $4 for the SPI-to-ethernet bridge module, DELIVERED! Or less than $2 for the DC-to-DC converter board.

Unbelievable.

Cheers!