These vehicles are known for cylinder head gasket failure, whick could e your coolant loss concern. If there is a head gasket failure, it is possible that it is saturating your spark plugs with coolant and fouling them out.
185k on the odometer, yes it could be a fuel pump concern. Remember, a fuel pump is able to give you pressure, though it will not have volume. My recommendation would be, if the vehicle cranks, check for spark, if you have spark, then put a small aount of fuel into the intake and see if the vehicle fires, and then continue with your diagnosis.
When a vehicle cranks but does not start, it is generally fuel or spark...sometimes it can be both. A failed O2 sensor will not generaly keep a vehicle from starting or running. The PCM would have picked upi that the was a concern with the sensor, turned on the service engine light and put the PCM in to what is called Fail Safe Mode. This is where the vehicle operates at set parameter's.