A Fullborn could certainly survive but not indefinitely. Compounding offers a vast amount of whichever attribute you want but it doesn't offer infinite amounts forever.
I've looked on Arcanum (admittedly only under the "lerasium" tag) and all I've found regarding this is: https://wob.coppermind.net/events/64-firefight-phoenix-signing/#e894
Which notes that it contradicts earlier statements but disagrees with your statement.
Why does that show inequality in the relationship? That's only referring to Vorin culture. If I remember correctly western Rosharan nations worship Cultivation.
Welcome!
Also an Aussie here, there are a few of us around.
For Cosmere theories and discussions this is the best place to be and hopefully you enjoy your stay.
A tip: be careful of the biscuits.
That might be less likely to work. Hemalurgy deals with the Spiritual and that seems like a purely physical situation, I don't think there's a spot in the spiritweb regarding how full your stomach is.
Each Order does have a polestone/gemstone associated with it. They line up as shown here: https://coppermind.net/wiki/Ten_Essences (technically none of the Orders are shown but their Heralds are plus the attributes)
Preservation.
Assuming I get to choose the time and place I'd happily keep things as they were at that time, at least things within my personal life and lives of my loved ones. It's shortsighted and selfish but it's the Shard I'd choose.
Running out of metals is something any allomancer has to face, it's like running out of ammo.
Why glass? It's easy to get, obsidian is less easy. Mistborn are assassins more than warriors on the battlefield, something heavier and larger would probably work against them.
Echolocation would require two steps IMO, one for hearing and the other for producing sound used in echolocation. I think tin steals senses when used hemalurgically but that might be all senses rather than specific ones.