Do you have to support a little county or a big country?
Short answer - everything ran fine on one virtual machine but it's easier to maintain on multiple machines.
Long answer - Our small county (40,000 pop) started with everything on one virtual machine - server, portal, datastore, web adaptors, IIS, and MS SQL. It worked fine, especially since we were not running any web apps then. The problem with having SQL Server in there was that I had to maintain it. We moved our database to the county-wide instance and got high availability (they have 2 or 3 servers, I forget), IT maintenance (updates and backups and moral support as needed). Since their servers are sized to handle the entire county's needs and ONLY run SQL Server, our puny spatial data needs had no impact. We also benefit from not being limited to 4 cores over there.
Then we moved each ESRI component to a separate virtual machine. So now each has 4 cores of its own, still complying with our license but giving us more than 12 cores instead of 4. (4 each for datastore, portal, and server plus the ones on the SQL Servers) IIS (and web adaptors) are still on the Portal machine.
Hope this gives you some useful info,
Brian