Peter the Australian government is super strict when it comes to visas for thai people, but the more information you give them the better the chance of being approved, so don't stress about a specific figure, they just need to know it is a real relationship, and you can afford to look after her for the duration of the holiday and most of all that there are reasons (example; own a house, have children there, have a job etc etc ) that she will definitely return to thailand once the visa is approved, while the questions sound intrusive which they are, provide them with everything plus some (photos, dates,facebook msg) everything to prove it's real.
Allowed 2 entries by land and unlimited by air, and pending when you return, the thai Government is changing from 30 to 60 day on arrival, not 100% Guaranteed after all it is thailand but end of June or early July this MAYBE implemented.
My partner was knocked back on her first attempt , the reason stated was they doubted she was in a relationship with me and doubted she would return to thailand if granted a visas , long story short got a visa on her second attempt, but you really have to convince them everything is above board and legitimate, that means photos with dates, text msgs with dates , screen shot of facebook if it's relevant, letters from family members backing your relationship anything and everything counts, yeah I know it gets very personal but if you want the Visa that's what you have to do.