Cloud Migration

One point of many is to utilize technologies that prevents access to those who manage the data/infrastructure/services but still enables owner of data to utilize it seamlessly.

An example of this principle is SQL Always Encrypted
https://docs.microsoft.com/en-us/sql/relational-databases/security/encryption/always-encrypted-database-engine

I think security must be the top concern of all...

So, it is better to choose a verified Cloud Service Provider before you surrender the control of your intellectual property. This will prevent your company from being on the wrong side of litigation.

Preparation for security concerns should be undertaken at the beginning of any cloud strategy which will ensure that the security of company's data.

Your question is very vague. The answers will differ depending on what you want to achieve in the migration, and how eventually your operation is going to look like. Consider the following:
* Cloud is used as a DR environment to an on-premise application
* Cloud is used to host internal applications for really remote users.
* The CEO decided to move the entire IT operation to the cloud
* Cloud is used only for test and development. Not for production workloads.
* Cloud is used only for big-data crunching

Although there is overlap, the issues you will face for each scenario are different.