The turbo pump is the main barrier to entry when making a large rocket engine. There's so much energy per unit volume that there is no failure mode that does not result in an explosion. Also keep in mind, you have very hot gas on one side and a few inches over cryogenic liquid oxygen. Liquid oxygen turns anything in to fuel so think about how to lubricate that shaft let alone seal it.
Another interesting thing to think about, it's the turbopump keeping the combustion from running back up the injectors. So, the turbopump has to outperform the combustion chamber in terms of pressure and flow rate.
Not quite literally, in e.g. Soviet engine designs some gas generators are oxygen-rich, they produce oxidized exhaust of high temperature, and the engine still doesn't burn (usually).
> So, the turbopump has to outperform the combustion chamber in terms of pressure and flow rate.
Yes, the injector pressure drop can't be too small.
Robert Goddard had terrible difficulties with fuel/oxidizer pumps. It wasn't because he was not smart enough. Most of what was needed hadn't been invented yet.
Another interesting thing to think about, it's the turbopump keeping the combustion from running back up the injectors. So, the turbopump has to outperform the combustion chamber in terms of pressure and flow rate.