I don't have all the answers, but I have some:

-I've uninstalled Poser completely (from my Windows Programs and Features tab, AND from allowing it to uninstall before I install the new version) several times between the many updates they have for us early adopters, including a couple of times that after uninstalling I went in and manually deleted the leftover Poser 11 folder and Poser 11 Content folder, and my preferences and preferred state are intact. As long as you don't go into where those preferences live in your User folder (or whatever it lives on a Mac), and when you install you ask it to keep using your existing preferences when it prompts you for that (like before, your options are to delete the preferences, to back up the preferences - which is the default if you just skip it - or to use the preferences), you're fine.

-On extra content: for now they're separate installers and I imagine they'll keep it that way, so you can simply not install those.

On what I'd imagine but can't say for sure:

-For your offline rig, I imagine you can simply download the installer on an online device, and take that to your offline device. I'm not sure how it validates your one-time Product Registration window though. You get a 21 day trial time, might be enough to set up some temporary web connection maybe.

-On waiting until november: well, it's an update. Pretty sure it'll be there waiting for you like usual updates.

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Feel free to call me Ohki!

Poser Pro 11, Poser 12 and Poser 13, Windows 10, Superfly junkie. My units are milimeters.

Persephone (the computer): AMD Ryzen 9 5900x, RTX 3070 GPU, 96gb ram.