Dear Chijl,
I would not recommend you proceed with this plan for a few reasons.
Working in private practice is very different to the public system. Namely due to the business pressures and knowledge of insurance protocols. After two years, you will not have had enough experience to develop sound enough skills to be a sole practitoner. You probably think you do but trust me you haven't.
Secondly, Even if you had enough experience ( I would say at least 5 years with at least 2 years of that having worked in private practice already), this set up suggested isn't a good idea. For one thing you are not really self employed if you are paying the GP in question a cut of you fees. You will be too tied that GP and the arrangement could become inappropriate in terms of the types of patients you see and how often etc. You wouldn't want the GP dictating how you treated your patients, you could lose your autonomy and 'feel the squeeze' in a far worse way than you ever felt working publicly. Besides, expecting you to pay rent and pay them a percentage is disgraceful. You should only pay rent.
Having no business experience is also a bit of a worry. It won't just all fall into place, and the chances of your receptioninst having all the knowlege you lack is incredibly unlikely. A medical receptionist has different knowledge and skills than a physiotherapist's receptionist. As a principle of a practice you need to know how the admin side of things work yourself even if you don't do it yourself.
I would recommend you find yourself a private practice job and see what it is all about first. Get a taste for the types of patients, probable shorter appointment times expected of you, probable remuneration by commission (therefore different pay packets every week), probably no annual leave or sick leave, probable evening and Saturday work, probable lack of inservice training, probable times working alone. Become familiar with Workcover, TAC, DVA and the extra paperwork.
I make it sound like Private practice is hell but it isn't. Alot of new grads and public employees just don't realise what goes on. University doesn't prepare you for private practice and it should. I have been in private practice for 10 years and it does have it's advantages. You have the chance to earn more money, you have more autonomy and you see more acute conditions.
Please consider your options carefully. I feel there are many more cons than pros with your proposed career move.
Good luck!!