Hello again,
If you want to have one company that will operate on the UK and EU market, then you will have to take care in preparing the initial balances for the new Cloud environment, because you will have to take care of double analytics of customers, vendors, inventory and other entries.
Of course, you will have to have localization for the country in which you will do business, which will cover all legal requirements.
With various native settings, you can make a difference between doing business with UK and EU clients, such as using different dimensions, or posting groups of customers/vendors or similar. You can differentiate general ledger entries with different posting settings, so that EU and UK postings differ if required by legal requirements.
Also, if there are different functionalities on the current NAV and BC on-prem environments that were used depending on the business market, then it will be necessary to consolidate all functionalities on the SaaS environment.
If you have any more specific questions, I am at your disposal.