Testing migration to cloud - Organization users

[Adam Beck]

I have a couple questions and Im hoping someone can give me some direction before I hit the button and do this wrong. Ive tried reaching out to Atlassian but my Loyalty Advocate has ignored me for the last month and is holding everything up. 

We currently have a Cloud Org and Site set up with Jira Service Desk management. This is production and is being used. Users are being synced from Google Workspace. This is all good.

We also have a Jira Software Server (and Confluence) setup. I need to start migrating these to the cloud. I want this to be simple, but so far there are some questions and I fear that if I hit go ill go down a bad path that I cant recover from.

According to this document: https://support.atlassian.com/migration/docs/test-your-server-to-cloud-migration/

I should test the migration in a organization, that is not my "production" organization. I understand the idea behind this, however two things:

I want to activate the cloud trial for the software to test the migration. When doing so I am asked to create a site, what organization is this site going to be tied to? If the user logged in, is not a org admin (of my current organization), will it create a new organization for that site to live under?

Second to this, I want to be able to verify that the migration will work with the Google Workspace users in place, as eventually, in my production environment is where the other production sites will live. Should the idea be that I create a second org, with a dev site (say site-dev.attlassian.net), recreate the Google workspace config and import, try to replicate my production environment as best as possible and then migrate the sites? Are there any issues with having multiple orgs connected to the same Google Workspace to sync users?

Thank you