You can check how many license units available with this method $SYSTEM.License.LUAvailable()

And next depends on the kind of application, you develop. If it's some web application, and you have to achieve it for web session, I would try using %CSP.SessionEvents with OnLogin event, check how many license units are available and who is logging in, and decide to decline the login.

If you need it for some else ways of connections, I think the best place would be ZAUTHENTICATE.

Look at this page, it may help you in understanding how to configure it.

If you need to store classes and mac routines separately, you can use

{
  "objectscript.export": {
    "addCategory": true
  }
}

In the case of different behavior for different types, and place only mac routines to the specific folder, use this.

{ 
  "obejctscript.export": {
    "addCategory": false,
    "folder": {
      "mac": "mac"
    }
  }
}

Yeah, It's a bit tricky. All the code in Caché really stored directly in the database. But with VSCode, code can be stored locally as files, for easy access and the ability to use source control such as git. After any save of the file related to Caché, e.g. Classes or routines, it will be sent to the server and compiled there.

Having a separate development server, and a production server are for sure is best practice, for sure. With no permission to edit code directly on production. And with having DevOps, will be possible to build a production version and easily deploy it, by some actions or events.

 Very interesting question, could you please raise the issue in GitHub repository for the project.

We would need a bit more details about it, what you have in your SourceControl Class, and what do you expect.

But, be aware, that this feature was not completely implemented at the moment. It may not implement all the features available in Studio, due to some differences in architecture.

Permission denied issues come from a non-root environment configured for the latest few versions of IRIS. And, so, you don't have access to folders, out of access of user irisowner, which runs IRIS inside. This user has access to his home folder - /home/irisowner, and /usr/irissys, where IRIS installed. But you should know that anything created on a filesystem inside the container will disappear after its recreation. And it's how it supposed to work. If you need access from outside the container to created folder, or keep it save even when the container re-created, you have to bind some folder on your local filesystem inside the container, with --volume|-v option (do not forget to give permission to do it in docker settings).

I suppose, there is no way how to run Community Edition directly if you have so many cores, at least, yet. And at the moment, you can use Docker or virtualization, and Docker I would say preferable way.

After a brief look at the tif format, it found to be quite tricky to get ImageSize.

tif(folder, filename) {
#define READWORD $sconvert(fs.Read(2),"U2",endian)
#define READLONG $sconvert(fs.Read(4),"U4",endian)
#define WORD(%val) $sconvert(%val,"U2",endian)
#define LONG(%val) $sconvert(%val,"U4",endian)

  Set fs = ##class(%Stream.FileBinary).%New()
  Set fs.Filename = ##class(%File).NormalizeFilename(filename, folder)
  Set FileSize = fs.Size
  
  Set Width = 0, Height = 0

  Set Identifier = fs.Read(2)
  If Identifier=$Char(73,73) {
    Set endian = 0
  } ElseIf Identifier=$Char(77,77) {
    Set endian = 1
  } Else {
    Throw "Bad Format"
  }
  Set Version = fs.Read(2)

  Set IFDOffset = $$$READLONG
  
  Do {
    Do fs.MoveTo(IFDOffset+1)
    
    Set NumDirEntries = $$$READWORD
    For i=1:1:NumDirEntries {
      Set tag = fs.Read(12)
      Set TagID = $$$WORD($Extract(tag,1,2))
      Set DataType = $$$WORD($Extract(tag,3,4))
      If (TagID=256)||(TagID=257) {
        Set Value = -1
        If DataType=3 Set Value = $$$WORD($Extract(tag,9,12))
        If DataType=4 Set Value = $$$LONG($Extract(tag,9,12))
        Set:TagID=256 Width = Value
        Set:TagID=257 Height = Value
      }
    }
    Set NextIFDOffset = $$$READLONG
    Set IFDOffset = NextIFDOffset
    
    Quit:(Height>0)&&(Width>0)
  } While NextIFDOffset>0

  ZWrite Height,Width
}

There are many different types of applications. And Caché or nowadays IRIS is just a part of it. For any new applications, I would not recommend using ObjectScript as much as possible and use it as a Database if you need it to just store the data. Any simple application may become bigger in the future, so, having already something that will help with is a good idea. InterSystems some time already offers Community Editon version of IRIS, which is for free, without some of the features, and limited by the size of the Database. And for a simple application, 10GB looks enough. But depends on what do you mean by simple application. It may do some simple task but which will be heavy in the size of data.