thanks for your positive feedback
1/ indeed lowest note of the keyboard when in octave -2, is number 12 in midi, and its equivalent in CV. We set Middle C (C4) on the middle of the keyboard, so lowest note possible with a 25 keys keyboard and 2 octaves transpose is C1.
By the way C1 is 32Hz, so probably low enough for most applications... But I checked MC4 manual, it looks like middle C is note number 24 by default, that very low compared to common synthesizers. I didn't dug into it, but it seems to be possible to change it. MiniBrute, and most modern synths are using 60 as Middle C. You could try to change it...
2/ If your gate selector is in KBD position, Gate In is forwarded to Gate Out, so if you use both, connected to an other machine you are creating some kind of feedback loop, and at the end Gate is always On. By the way why do you use Gate IN if you play build in keyboard? Don't plug gate in, and your MiniBrute will respond to the keyboard, without feedback loop.
3/ The pitch applied to the VCO is the sum of keyboard tracking and PitchCV (plus LFO, Vibrato, and PitchBend), so indeed if you press a key on the keyboard, it will transpose PitchCV. If you want to be in tune, you need to press a C key. As stated in question 1/ C0 is not possible with built-in keyboard, but there is a workaround: at startup MiniBrute defaut pitch is C0, so if you don't press any note, incoming pitch CV will not be transposed.
So no real solutions to your problems but at least, you know what is going on inside....