How to organize the relocation of the IT infrastructure of the company to the data center?

Question

System administration

There is a task of transferring servers to a data center and organizing the work of company employees through a terminal client. The main question is how to properly design the IT architecture in the company in order to:
• Ensure a smooth transition without stopping work
• In the future, it would be possible to increase the number of employees without global rework
What we have now:
Office and remote employees 25 people
Services used:
1. Terminal server 2008
2. Domain controller 2008
3. !c (win 2003)
4. Mail server (linux)
5. 2xFirewall (linux) one in the office, one in the data center
6. Asterisk (linux)
7. Backup
8. Two oracle databases, very modest in terms of resources (4GB RAM, 2 CPU, 300 Mb HDD)
9. File server (shared file storage)
10. Website
Now all these services are virtualized for different hypervisors (vmware, kvm) and different servers in different data centers.
There are actually up to 20 thin clients in the office, the same number of IP telephones, a printer, a scanner ... .. There are also a number of “ wishlists
” from the category:
minor edits), powerpoint
I ask for advice, is it right to do this:
1. Find a specialist who will assess the required resources in more detail and “draw” the desired architecture, including hardware requirements, one type of virtualization, etc. (the main question is where to find such a specialist)
2. Install hardware in the data center
3. Select an organization that will have to configure the virtual infrastructure and maintain (administer) it in the future
4. Transfer services to a new location

Answer 1

item 1. - Yes, and it should be the same as item 3 (or preferably)
The remaining items are irrelevant after item 3.
item 3. The contract, a clear statement of work, the press of money.

Answer 2

Please advise if this is the right way to do it:

Whether it's correct or not is up to you. The main thing is to find such a person or company, but in general, I don’t see any problems at all in order to give it to the side.
Under your case, hyper-v fits very well.
If you all sit in the terminal, then in general you don’t need to take out AD separately as a cache.
You can also organize graphics rendering via RemoteFX (essentially the same RDP)
Example of work:
https://www.youtube.com/watch?v=MUrY3_lqK2Q
Here, for some things, you can think about renting a server in a DC.
But it is necessary to more clearly present the task.
It's easiest to do it in stages.
But I have other questions.
What if your server goes down for example? How much your business will be able to endure 1-2 days of downtime? If you are planning multiple servers, then it makes sense to consider clustering, and Hyper-V is again generally suitable for this. You can use continuous replication for backups. The question here already goes further, about the reliability of data storage, etc.