The treated should work. Put copper green liberally (politics rears its head) on the end of the post where you cut it.

If you want to do the pedestal effect later, you could mock it in. Depends on how groovy you want it to look.

I looked at photo #2 again and I don't see why you couldn't put at least one pillow block under each of the those wide runs. I would normally run my joists the short way.

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Te futueo et caballum tuum

1986 300SDL, 362K
1984 300D, 138K