I was in a similar situation to yourself. The best thing i can suggest is doing your farm work, and then live together for an extra year. Its a MUST that u have to LIVE together, not be together for 12 months before u can apply. If u dont meet this, then dont waste your money and apply cause it will be refused. You need to prove more than just going out, provide as much evidence as u can. We submitted joint bank accounts (again a big thing they look at)., joint gym memberships, trips/holidays out together, evidence we share things ie groceries (we put like 30 bucks a week into our joint account). Stat decs are great to use, but the DIAC will look at your co-habitation over anything else. As for registering your r.ship, just ring up and make sure.....because i was in melbourne and to register a r.ship u BOTH have to have resided in melbourne for at least 12 months before u can even apply. It might be diff for NSW or QLD, but u cannot register a r.ship in WA. I would deffo apply in Oz and do farm work, could be risky coming back on a tourist visa unless u have proof u are going to travel and DIAC may question your reasons for coming back to Oz, after being here for a year... or just both go home and apply from the UK if this suits.
I had the help of an agent and he said u have to prove u are more than just boyfriend and girlfriend. Hope this helps. Feel free to inbox me