Do you plan to ever use the heater? If so, use a 180. A 160 won't let the coolant get hot enough to produce much heater output. If your radiator is a zero pressure unit, using a 195 stat pushes the minimum temperature a little too close to the boiling point.
Yes, the system needs some kind of thermostat, or at least a restrictor disc for flow control, regardless of what some self-appointed "experts" have to say.
Jerry
