"Most of us are amateurs-in-learning :) (I certainly am). You can buy a 5v BEC from any drone/hobby shop, as long as it does 2-3a that will take care of anything a raspberry is likely to consume. A lot of PDB (power distribution boards)…"
"Pixhawk fits in the underneath bay perfectly but then you can't put downward facing payload. It will fix in the nose bay fine but makes it a bit difficult to balance the CoG with the battery. You'd be much better off with a pixracer…"
"Depending on what you mean by drone, and what type of work you're doing, no you don't need a lidar or any other rangefinder. Rangefinders are useful but not mandatory. Altitude hold is done primarily by barometric pressure…"