you must have the following points- Center, Aura (-Y axis coordinate, this is below the Center), and Above (just what is says, but it must be DIRECTLY above the Center).
Exhaust is the engine effects. Other particle effects are ability points, bombing points, and weapons points. Ability points are only necessari for certain abilities; bombing points are only necessary on something that can bomb a planet.
Buff points, not sure what you mean what this is.
There isn't a mandatory number of points. For all intents a purposes, a mesh only NEEDS 3 points- Center, Aura, and Above.