Part 91 IFR takeoff
 

In part 91 do you have to have the take off min to take off. Or can you take off with 0/0 under all circumstances.

No minimums. Might want to make sure you can get back into the field if something happens though so a 0/0 departure is not a wise move. Plus, it's probably pretty hard to find the runway in the first place.

In a single-engine airplane, I require enough visibility & CIG to land off-airport following an engine failure. The exact VIS & CIG would depend on terrain.

In a multi, I want to be able to return to the field OR reach a nearby field very quickly. The SOCAL marine layer may shut down my airport, but there are several within spitting distance to the east that would not have the marine layer problem.

Basically, the higher the ceiling, the more time you have to choose a suitable emergency landing area when the engine quits. The FAA leaves it up to us to use good judgement.

All is good unless somethig bad happens. Then you get slapped with carless and reckless operations.

Yeah, the FAA will give you the rope "0/0 takeoff", and let you hang yourself.