Hello, your advice and help would be most welcomed and appreciated

My girlfriend and i have decided to live together and we want to do so in Aus. We eventually want to get married but want to trial for at least 12mths.

We are both over 30 and i am an Aus citizen and resident.

Is it easy to get a student visa whilst in Aus on ETA tourist visa? (on shore)

Then how hard or easy is it to make application for on shore 820 spousedefacto Visa whilst out here on student visa?

thank you