Since any child will be a UK citizen in its own right (child of one UK citizen and born in the UK) I don't think it will count in terms of upping the financial support we will need to show to get the ILR since the UKBA can't deport it - can anyone confirm/deny that this is the case or will a child have visa implications on that front?
Since you will be on the old rules, there is no minimum financial requirement for ILR.
You just have to show that he has not accessed public funds in the 2 years on FLR(M) and that you can still support yourselves without public funds once he has ILR.
Also, does Maternity pay count as income or benefits for the purposes of applying for ILR, i.e will the maternity pay I receive during my leave count as income that I can put down and use the payslips as evidence of my income during the period I'm off, or will the UKBA class maternity pay is a state benefit and decide that my receiving it is evidence of my not earning but being on state benefits during that period? This is important as if my maternity pay is not counted (or worse, counted as a period our family required state support) as income by the UKBA we may have problems meeting the financial requirements (with it we're OK on that front at least).
Again, there is no financial requirement to meet for ILR - you would just need to show you have enough income that your husband won't need to access public funds (you and your child(ren) can claim any public funds you are entitled to).
Maternity pay and maternity allowance are not considered benefits anyway (i.e. they are contribution-based so are not considered public funds and can be claimed by someone on a visa), so that won't make a difference to the application (see here for what is considered public funds and what isn't:
http://www.ukba.homeoffice.gov.uk/visas-immigration/while-in-uk/rightsandresponsibilities/publicfunds/).
All income will count, but as I said, there's no official financial requirement - as long as you can pay your rent and council tax and still have enough left over to live off, you will be fine.