Perhaps check with your local council to see if they have a plant list. Many councils here in NSW do this to assist homeowners with choosing native Australian plants and some introduced plants that grow well and are in keeping with the area. Of course it depends on the look of your house and whether your landscaping plan will compliment that, or whether you want a manicured look, or a natural look, cottage garden look (e.g flowers and hedges) or a beachy look (e.g. if you have a pool) and so on. Fruit trees sometimes need a different aspect to other trees, so separating food trees from general foliage is something to consider. Oleanders are off the list in many parts of NSW too. We recently put a fence in similar to yours but it has been painted black as our house is modern. We've been advised on lomandra, banksia and grevilias and lili pillys for a native garden as we already have lemon scented gums and ironbarks on the property. If you consider the building style of your home, and the trees common to the area you're in, sometimes that can give some inspiration

Before replacing your curtains as this can be quite expensive for such a large window, if they are in good condition, add a band of extra fabric to the bottom in what ever suits you, your existing curtain track can then be moved up to the ceiling for good looking full length curtains without the large round eyelets, could save you a lot of money, I would look at replacing/removing the sheers cheers

Granny Flats (secondary dwellings) to me are afterthoughts. Its the thing you add to an existing dwelling. Therefore if possible do a duplex if its possible in your area. Secondary Dwellings cost as much as any other similar sized dwelling. Many think that as they're so small they should be really really cheap....

It probably depends on where you live. If there are lots of families then i think the 4 beds would be the preference, 3 brms are a lot more common so often 4 commands a premium. An ensuite is always desirable but i would probably just look at converting the linen into another toilet. And create built in storage in all the beds