Answer:
I would say preliminary and incoherent.
Step-by-step explanation:
Since the objective here is to guess the meaning of inchoation from the context, we should take in consideration that the author gives us a poetic tone for the pleasure of good reading, describing this feeling as something nameless, inexplicable, incoherent.
And the preliminary aspect is deducted from the beginning when he/she begins 'one both anticipates and fears...' and later at the very sentence where ' inchoation' appears - the inchoation of our experience that is suddenly given shape and form. Since it suddenly takes shape, this feeling he/she describes is early, initial, preliminary!