Hi Ted,
I think DShot is a good choice although I don’t personally use it on my multicopters (yet) but I am using it on my boats. blheli32.com seems to be down (and it’s been down for a while now) but it use to provide a list of compatible ESCs… no idea what’s going on there but personally I use these DShot ESCs from holybro (I should add that HolyBro sent me them for free). I’ve actually heard from other devs that the Turnigy ESCs which appear on our DShot wiki page are not recommended.
ChibiOS is stable and it does perform better than NuttX (faster and more consistent update rate). I have not seen any crashes caused by ChibiOS issues in some time. NuttX has been removed in “master” so all major releases (i.e. Copter-3.7) from now on will use ChiboOS instead of NuttX.
Old Pixhawks should all be able to run ChibiOS with the exception of the very very old two-layer Pixhawk1 which almost nobody has.
Telemetry is not stictly required