It´s definitely important to have or use a good piano if you want a future as a pianist. I don´t really care much about the sound or the condition of it, as long as it doesn't hold you down, and I think you will notice if it does bother your technique. It´s mostly about being too familiar with your own awkward piano and the certain technique you use for that piano, which might not work with other "standard" pianos.
I guess that´s another good thing with having a piano teacher. You can visit her nice apartment somewhere in Austria, and play Schubert on her nice grand piano.
I fell victim for this fact once actually,because I began playing on an electric piano with very light keys. The ability to use powerful dynamics was pretty useless with a piano like this, and I played with my hands quite high above the keys, not pressing the keys down enough. I got a very (pardon me) "Chinese" technique, quite the opposit to the russian technique.
The next piano I got was "real" this time

, but VERY lound. The electric piano was bad at discerning voices and velocity, the sustain pedal was very kind to me, and the piano was generally quiet. The real piano was not. It was very good, but very different.
The loudness and uncontrolled sound randomly comming out of this piano was because I didn´t know how to handle a real piano. Because of this, I played every quiet/piano part with the use of the soft pedal. I realised that this method was stupid, and for two years I had not yet been near perfecting the art of pedaling, dynamics, pianissimo and the "push down" technique. And my scales were horribly uneven.
I know Chopin said/wrote/sang/meant that piano students should make sure to practise on a good instrument.
On the other hand- If you can rein a bad and wild piano, then playing on a Steinway concert piano should be OK, once you get used to it...