1.)Are all the vehicle manufacturer recommendations necessary?
Yes, they are suggested to help you avoid a break down. Not all breakdowns can be avoided. However, if you properly take care of your vehicle it greatly reduces your risk of encountering one.
2.)How easy is it to blow a head gasket or motor?
All it could take is one time of overheating to severely damage your vehicle. It is always a good idea to understand how all of your gauges work, what they are there to tell you, and watch them while driving.