HI
As far as i know
The visa you are looking to apply for could take up to 6 months to process. This don't include any of the time it takes to get all the relevant checks and medicals organised and back to lodge with your visa application and at this time of year i would have thought your pushing it.
If you apply in England you can pay with Australian $$ no problem. I'm sure you can use your AnZ card or Nab or who ever
To become a citizen you must
have been living in Australia on a valid Australian visa for four years immediately before applying which must include the last 12 months as a permanent resident, and
not have been absent from Australia for more than one year in total, in the 4 year period, including no more than 90 days in the year before applying.
My sister 13 years before me and myself found anything to do with leaving the UK extremely difficult in the UK. However that is not to say that its going to be any more or less of a challenge for you.
Hope this helps