Welcome to United Bimmer.
If I recall correctly you have the M52 engine in your vehicle. The M52 had a cooling system that was notorious for failing. The water pump (pre 1997) had a plastic impeller which would implode with age. The thermostat housing was plastic and would crack. The coolant expansion tank was again plastic and would become brittle and crack. The best replacements for te water pump and thermostat housing are aftermarket aluminum ones. now where exactly was the coolant? Near the radiator cap? It's possible that if you had never changed any of those components one of them likely failed. I had my thermostat stick open once and I had to limp it home cause vit would get close to overheating very quickly. That is most likely what happened if a hose didn't come loose.
As for the lack of power and stuttering that could be a vacuum hose that has come loose or cracked. A sputtering or sporadic idle is usually cause by By a crack or hole in an airline. Unfortunately their are a number of lines in the engine bay. However if you look carefully enough and feel them for cracks or tears you should be able to find the issue.
Let us know if this helps!