Data such as email is fairly easy, but apps can be a headache if not prepared. Once you’ve chosen the best cloud vendor and migration partner (your IT support provider), use those resources to determine what needs to be done to integrate your infrastructure with the cloud. Constant testing is required, although with every month the process becomes more ‘push-button’ (NOTE: ‘more’ - NOT ‘completely’).
Presumably, your IT services provider has mapped out everything from Storage I/O requirements to CPU usage for database requirements to backups, business continuity and disaster recovery management. Without having this work already done by a qualified cloud migration expert/IT support and services provider, don’t expect it to run smoothly, because it most likely will not.