I would like to know whether there would be a good enough chance of a visa being granted with no immediate proof of living together for the last year - although we are now living together. Would I be wasting my time and money - is it worth waiting for another 2-3mths to build proof or not?
Almost certainly there's NO chance of getting a visit immediately, yes, it would be a waste of money to try straight away, and yes, you need to build up some proof. When you submit towards the end of your partner's visitor's visa, THEN some of the old evidence will be useful background, but that's all it can be, since INZ have to look at the most recent time leading up to the application.