Considerations during website migration and domain change

Hello

I would like some assistance in understanding all considerations and best practices that we need to account for as we go through a website domain migration.

We have used Marketo primarily on www.passageways.com and have a new website active onsembleintranet.com. In the coming months we will have another website bringing the total websites on this instance of Marketo at 3. What will this entail?

1. 3 Websites
2. 3 email domains
3. 3 Brands
4. 2 Teams
5. 3 Regions

I would like to understand what we need to account for through this transformation on the following accounts. Also what else is there that I am not thinking of?

1. Installing Websites into Marketo?
2. Best Practices for Databases?
3. Best Practices for Subscription Centers?
4. Implications on current lead scoring?
5. Email Deliverability testing for all 3 domains?
6. Design Studio Considerations for all 3 brands
7. Testing and QA of Staging websites before brand launch.
   
   Hoping that someone can help me piece together the various aspects of this project, what questions to ask etc.
   Regards
   Lopa