We're migrating our enterprise instance (5000 JSW, 4000 Confluence, 1200 JSM) from Datacenter to Cloud now and it's a mess. Less functionality in Cloud, plug-ins that partially migrate, etc. it's just not a clean migration. But we're working through and we'll be done soon.
The next step is to start consolidating instances. We have at least 9 different instances ranging from 25 users to 1000 users. I'm looking for an overview of Cloud to Cloud migrations and any information would be helpful. Ignoring plug-ins because I understand each plug-in can bring an entirely separate complexity to the migration, but is Cloud - Cloud relatively simple/painless assuming you've verified project keys, custom fields, etc.? Or is it just as much of a mess as DC --> Cloud?
What timeline should we be estimating for Cloud > Cloud (again ignoring plug-ins) assuming we have no key overlaps? Is it a 2 week project? Or 3 months?
How does licensing work? If we're using 4950 of our JSW licenses and we migrate an instance with 65 users, do we gain their licenses and users? Or do we have to bump up to the next tier?
Is any/all of this documented somewhere? I haven't found very detailed migration documentation, just https://support.atlassian.com/migration/docs/perform-a-cloud-to-cloud-migration-for-jira/ which makes it look like it should take a few hours.