DIY adjustable buck boost converter with serial interface
With a sufficient input voltage supply (i.e. 70 volts) you don't need a buck-boost regulator so just consider a buck like this one: -



Getting the output down to 0 volts requires extra circuitry but maybe 0.8 volts is sufficient? Controlling from an MCU would require some external circuitry and possibly consider using a digipot but there are other ways to skin a cat such as injecting a voltage into the VFB pin via a high value resistor from a DAC.

Using the MCU controller and DAC/Digipot means that other pins of the MCU can be used for a serial interface.