Migrating to AWS with Devops
Continuous Deployment is certainly a no brainer for mission critical applications but you may try Azure DevOps from MS which integrates with AWS beautifully and has provisions for environment approvals which can help move to that state in a user friendly and elegant manner. IMO, AWS code deploy is still not at par with Azure DevOps. And perhaps you may want to incrementally move there and refine your used case.
e.g. Instead of weekend deploy, you can make the process decoupled and efficient that you can do it on a Friday night, then setup blue/green in Beanstalk or EKS et to reach that state. Also for the 6000 hosts, you definitely want to try and see which can live in Kubernetes for ephemeral instances and review the infrastructure footprint. Don't forget cloud is expensive, a lift and shift of that many VMs would have exponential costs in cloud.
I work in healthcare so unsure about retailers, but thought I will suggest that tool (Azure DevOps) incase your client isn't familiar with DevOps for easier transition.
Also to be more comprehensive, consider monitoring, security etc also as a part of your effort in your white paper.
One of the most comprehensive DevOps roadmap (evolving) is this, you may consider all the aspects from this chart for your whitepaper -
https://roadmap.sh/devops