I'm not sure about the details for some of your questions - it might depend on whether you are in the public or private sector - with the 14 weeks paid leave I'm assuming you're in the public sector. If so you can check the relevant state legislation - public sector management act or similar as it will have policy around mat leave.

I'm sorry but I think your boss's attitude to not wanting to discuss this in terms of money is ridiculous and unfair! Perhaps he is unsure of the guidelines that apply to you? Every person in the paid workforce enters a 'contract' with their employee - I turn up for a set number of hours per day/week/shift, complete set/defined work tasks and receive a set/defined weekly or hourly wage in return. I think you can demand (or ask nicely ) that he sit down with you and discuss all of your options and choices in detail, including rates of pay.

I would also contact the union for your particular industry and get some independent advice from outside your workplace.

Good luck!