Q2, not sure if I explained this one before ...
It's operating in the 'common base' configuration which can also be called cascode (*). Current fed into the emitter simple appears at the collector (well, most of it). Put like that it seems kind of pointless but the usual purpose is that it mitigates the 'miller effect' of the transistor feeding in current to the emitter since the voltage there barely changes. The cascode transistor itself still gets effected by its BC capacitance (its collector voltage is changing) but it is not being multiplied by gain so its a win-win.
In this 'design' that aspect is probably not necessary. But, if you look at the specification for HV transistors, you will see the gain is very poor (a reason why people like valves for HV?). For this design I was trying to mitigate poor gain by using a low voltage / high gain and high voltage / low gain pair to get around it. Time will tell if that works out
dc
NOTE * Yes cascode and most definitely not cascade. I once found myself joining a lecture given by a really good Czech electronics engineer to 1st year UG's. At the end of the lecture I noticed them scribbling away and mostly looking very puzzled so I inquired what was so puzzling - I thought he was very clear. Turns out that, thanks to his slight accent, they thought he said cascade when he had actually said cascode - which they had never heard of! It was funnier at the time!