Well, I can answer a bit:
Your first and third questions are related, as you can't chain layouts using the meta tag.
Your final page should have a meta tag as you suggest, but if you want to layer a layout on top of another layout, you put a g:applyLayout tag at the top of the child layout, pointing at the parent.
In your edit.gsp, you'd have:
<meta name="layout" content="editTemplate" />
and in editTemplate.gsp, you'd have:
<g:applyLayout name="baseTemplate" >
<!-- the html for the editTemplate -->
</g:applyLayout>
so edit.gsp would use editTemplate.gsp, which would use baseTemplate.gsp as a base layout. You can chain those as needed.
I haven't used g:pageProperty at all, so I can't throw you better examples there, sorry.
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