what is the distance from the existing house to the boundaries on all sides, where is north, describe your local climate, do you want a garage or carport, where is the driveway entry from the street and what are the floors, walls and roof built out of?

North arrow shown on photo with aerial. Climate is Melbourne suburbs. No garage or carport necessary.

Doing a decent size extension in two stages would require a lot of planning to do the stages so you don’t double up in costs. Our Council’s permits give you two years to start the second stage. If you don’t you need to start again with the plans and permit cycle. Let along finding trades for a second round. This can be quite costly. You also have the inconvenience/cost of living through two Renos or moving out and renting. There are also economies of scale when doing renovations. So carefully consider your plan and what you can do all in one hit. I’d be aiming for two bathrooms. A renovated house 3br home with only one bathroom will suffer in comparisons.

pending more details my suggestion would be to have a bigger kitchen with pantry as the dining area feels too cramped, use the old dining as a separate study bed 4 with two living areas and consider a future master suite extension instead of rearranging the existing living area.. when you have such a good sized block of land extending at ground level is far more cost effective than a second storey that uses so much space with stairs

and, as big reader has already suggested it's cost effective to have plans drawn up and r Development applications submitted for both extensions and the alfresco even if you don't complete them all at the same time...btw having the new northern kitchen wall line up with the northern wall of the original master bedroom would make the roof work better and not needing to make space for the dining area on the west gives more flexibility with the size of the kitchen family room