You would use a 5V supply (like V USB) to power the DAC and a level translator like 74AHCT125 to convert the 3V3 Teensy logic to 5V0. You would also need something like 4.7μF + 100nF supply bypass caps on AVdd.
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For CV out you do need DC accuracy which means audio DACs are not a good choice. Have a look at something like the DAC8568 from Texas Instruments; it gives you eight reasonable quality 16-bit outputs (4LSB INL, 0.004%...
Good to see the platforms (MacOS X, Linux, Android) building support, but there is still not a single MIDI 2.0 controller on the market (that includes the somewhat flawed Roland A-88Mk2 which maybe, maybe is hiding...