Just so everyone knows, archive.org automatically crawls sites and makes page snapshots when it sees that something on a page has changed. You don't submit your site. It happens automatically. When it take the snapshot it creates its own URL for that page.
For example. https://web.archive
The first part of that is the archive.org URL with the date and time of the snapshot. i.e. 20180206213750 The remainder is the original URL of the captured page.
Our static pages like the tech articles haven't changed in years. So we can copy the content from the archived tech article pages at any time to recreate them on the new forum. We don't need to do that right away since we can always grab the content later. (caveat about search engine traffic below though). There's no need to save anything as PDFs. The PDFs wouldn't really be useful on the new site anyway. PDFs are also difficult to copy content from because of the way they handle text flows and line breaks.
For the forum threads, if you look at archive.org you're seeing the recent posts on the front page the way they were on the day it took the snapshot. But the forum threads are constantly changing. You can browse around to a certain extent and click the forum categories and such, but the forum posts themselves aren't archived. That's the reason for making our own backup of the forum on our own server. All of the posts would be saved at the point when we did transfer.
I think getting the stuff in place to make our own backup and archive of the forum should be first priority. We need to get a web server lined up, and then work with Gram to get the current site's files and database migrated over there to make sure it all remains available.
My suggestion would be to get our new VB site ready. The new forum on VBulletin Cloud can be set up ahead of time. Assuming we begin with a default or pre-made theme and minimal organization it wouldn't take very long at all. Just get the initial configuration done. Forum categories and such. Then test registration and logins. Then as soon as we confirm that we have the current RSC archived we shut it down to new posts and registrations. The roadstarclinic.com URL then gets switched to the new VB site and we all start registering our accounts and start/continue our conversations over there.
But we will take a hit on organic search traffic. All of the pages and posts on our site have specific URLs that turn up in search results. After the switch those URLs will be invalid and would typically return a 404 page error. This won't really affect us since we're already here and familiar with the site. But for new members that are looking for info, and advertising it would be an issue.
But I think that if we put the archive on a subdomain, like archive.roadstarclinic.com then we put some notice at the top that links to the archive in case someone wants to look up old threads. We can set up an automatic rewrite for all of that organic traffic to point to the new site.
For the static pages like the articles, we'll have to create some specific redirects. For example, the tank removal article's URL is http://roadstarclinic.com/content/view/69/94/.
The VBulletin URL for that article will be different. But with a redirect in place, anyone that is trying to get that old URL will be automatically sent to the new one. Google likes it when that happens. Google doesn't like dead URLs that simply return a 404 error.
I'm glad that we're moving forward with a plan, but let's not make it more work then it needs to be.