CloudFormer[0] might be able to automate some of the process - it analyzes your existing VPC and generates a CloudFormation[1] template. You could then take this template and deploy the stack in your new account, and you'd only have to rebuild the remaining few items.
Then you could redeploy all your applications, test, and migrate production services to your freshly-tested instance. Finally, you must be aggressive in shutting down the old services. It would be agonizing to have your entire site down because one server remains in the old account, and the account had some issue. Feel free to contact me for more specific advice.
[0] https://www.linkedin.com/pulse/how-why-use-aws-cloudformer-a...
[1] https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGui...