What is the best way to upgrade the Windows Server infrastructure?

Question

Microsoft Exchange

Need advice on how best to update the company's infrastructure without cost overruns. The company has about 20 users.
There are currently 3 servers of the Core 2 era:
Server 1 (4 core Xeon, 4 GB RAM):
- Windows Server 2003R2 SBS
- Exchange Mail Server (role in SBS)
- Primary Domain Controller
- File Server
Server 2 (2 core Core 2, 2 GB RAM):
- Windows Server 2003R2
- Secondary Domain Controller
- WSUS
- File Server
Server 3 (2 core Core 2, 4 GB RAM):
- Windows Server 2003R2
- Terminal Server 1C Accounting/Enterprise (5-10 users per jump)
- File server
Given that Server 2003 has completed its life cycle, the question arose of what to update this whole thing for and what licenses to purchase.
If we exclude accounting, basically all users work only with mail and transfer some of their files through public folders.
It seems that it would be possible to upgrade SBS to Essentials, but it is not clear how to fit it into an existing domain without recreating it from scratch, is it possible at all.
Additionally, the transition to a stand-alone Exchange confuses, which also requires almost a separate server without the role of a domain controller, in our case, overkill. Plus, Exchange on SBS has a POP3 Connector for collecting company mailboxes from POP3, but it seems to be missing in new editions.
Please advise how this problem can be resolved?

Answer 1

Upgrade
installation An upgrade installation preserves the files, settings, and applications installed on the source server. You upgrade in case you want to continue using the same server hardware. You can only upgrade your existing version to Windows Server 2012 from x64 versions of Windows Server 2003, Windows Server 2003 R2, Windows Server 2008, and Windows Server 2008 R2.

I would advise not to update - there will be big problems with exchange (and at the same time get rid of the old trash on the servers), but set up again in the following sequence:
- "Server 3" do backups + uploads from 1s - Setup 2012 + 1s
- "Server 2" We set up 2012 and make it a domain controller
- and then we take on the most fragile "Server 1" I
advise you to install and test configure 2013, since it is very different from 2003 and 2010 but good, or wait for 2015 (coming soon)