MTR,
Most councils will require you submit a landscape plan, this includes a drawing with number and locations of plants.
I paid $6K for a 80 lot site, ensure you get it done electronically there are still some cowboys drawing them by hand. If you have a layout change you have to get the whole thing re-drawn. This plan has other uses than just an approval, it may be used to sell off plan as it will be the best looking drawing of your development that is until you get marketing ones done.
You may be able to submit a DA without one, maybe the council wont ask for it or maybe they will. On the Gold Coast a submission would not be classed as "a properly made submission" without it.
I don't accept POA as an estimate, all costs should be fixed regardless of how much your consultant complains about fixing it. You don't need more risk.
I would expect for every consultant you will have 2-3 fee proposals, this is what you are paying the architect for.
Mark