I think this line will be one of those "we are building railway line here", development will done around it.
Nah, that's not going to happen. How can you develop around all-night freight corridor which will only get busier and noiser? How do you develop around the rail line when the majority of suburbia is already there and built around the Mt Lindesay Hwy corridor? If it's being built for Flagstone only then it is a huge waste of money when it could and should be serving that entire 5-10km wide Mt Lindesay hwy corridor.
For the money you will save you could build the houses and give them away for a cheap price. If you resume say a km of 1 line houses that follow a road, average spacing of 25m each = 40 houses x $500k in purchase and compensation = $20m, then road diversions, other compensation, infrastructure relocaton etc etc quickly sends money over $200m/km going by recent projects. this compared to following an existing corridore. Viaduct construction is about $20m/km just for the viaduct, tunneling much more. unfortunately a corridore was never left for rail. probably why Springfield is getting their line over areas much more deserving.
This rail corridore moves about 8 trains each way per day, increasing by 100% (unlikely to happen in next 20 years) still makes it just 32 trains a day. The more noiser locations can be controlled. The alt you want to provide two rail corridores, one very busy by day and evening, the other mostly at night. And for those in the middle? One of the avanatages of combined road and rail or in thise case rail and rail corridores is noise is constrained to one corridore.
I agree divert where possible and practical as close as possible to the 'burbs and existing population, but a modern line this far away from CBD is never going to have significant "walk up" traffic as the station spacing is usually further apart (~2-3km) and stations are larger footprint to cater for park'n'ride, bus interchange, kiss'n'ride, taxi's etc.
AR has alot of development to nth of line
Algester to south
HillsCrest/Browns Plains both sides
Greenbank, there will never be much walk up traffic here in near future but progressively large blocks may become smaller, but large catchment both sides
Flagstone/Undallah, Flagstone is developing, Undallah will not be far away
From here I would divert from SG and also reduce tracks to single track to Beadesert with passing loop and platform at Cedar Grove.