Niki112 - itis really a challenging task to get - by calculation - a rough information for the amplitude of an oscillating system if a sinusoidal form is desired.
This applies to all oscillators.
The reason is: Each oscillator requires a certain amount of non-linearity for limiting the loop gain LG for rising amplitudes to LG=1.
Such a non-linearity is necessary because for a safe start-up of oscillations we need LG>1 for small amplitudes .
Hence, an exact calculation requires a system of non-linear diff. equations.
Therefore, you only cann make an assessment for the amplitude - based on loop gain information: (1) amount of excess gain LG>1 and (2) degree and form of non-linearity.