House design

We are going to gut our house and start again. There is one wall that is brick and cannot be moved as well as one arch way of brick that cannot be moved, as for everything else we just want to design our forever home that will be suitable for our family.
Things that are a must:
Bathroom (possible spa)
Separate toilet
Large main bedroom with large walk in robe
3 other bedrooms with built in wardrobes
Large study/office
Large loungeroom
Kitchen with views of front yard
Dining room
Linen cupboard/ storage cupboard throughout house

The current open fire place cannot be moved and I would like it to stay in a common area.
Any other questions please ask we also have an attached double garage currently being used as a games room and an undercover area at the southern corner that can be utilised and made the most of that adds another 6m x 9.3m to the floor plan, I actually wouldn't mind utilising this area and incorporating the games room and patio area to the house although there are 4 steps down from the house level at that point.

I have uploaded a current plan of the house layout with the 2nd picture showing the circled RED walls are the ones that have to stay.