Your situtation is pretty tricky . Amount of maintenance will depend upon how much motivated you are and how much effort you put - your case has all ingredients where you can minimise maintenance or nullify it alltogether - produce all the fixed expense details to the court - the rent receipt, child expense etc.
Once you are able to take out fixed expense there will not be much difference in your sallary and her sallary - and you will have a strong case for making maintenance nill.
Also to presurise her. Demand maintenance for your child.