Ens, EnsLib and EnsPortal are system packages, developes can subclass them.

To get class count call something like this:

SELECT 
  count(ID)
FROM %Dictionary.ClassDefinition
WHERE 1=1 AND
      System = 0 AND 
      NOT (Name %STARTSWITH '%' OR 
           Name %STARTSWITH 'Ens.' OR 
           Name %STARTSWITH 'EnsLib.' OR 
           Name %STARTSWITH 'EnsPortal.' OR 
           Name %STARTSWITH 'HS.' OR 
           Name %STARTSWITH 'SchemaMap')

Missing: SQL way to filter out mapped classes.

Use a Business Service with a basic Ens.InboundAdapter:

Class test.BS Extends Ens.BusinessService
{

Parameter ADAPTER = "Ens.InboundAdapter";

Method OnProcessInput(pInput As %RegisteredObject, Output pOutput As %RegisteredObject) As %Status
{
	$$$LOGINFO("In OnProcessInput")
	Quit $$$OK
}

}

Add it to production and set Call Interval to X seconds (and Pool Size to 1). That would ensure OnProcessInput being called every X seconds after it's last completion.

Component status

Use Ens.Director to get enabled/disabled and status:

set enabled = ##class(Ens.Director).IsItemEnabled(bh, .status)

Queue depth

SELECT 
  Name, 
  Count, 
  Created, 
  Active
FROM EnsPortal.Queues_EnumerateQueues()

Last activity date

Do you see it in SMP somewhere?

This is a limitation on a maximum resource length that was lifted in 2022.2 preview 4.

I would start by observing the output of these two commands when run from a Dockerfile:
 

set sc = ##class(Ens.Director).SetAutoStart("GOJ.IrisApp.ProductionDev")
write $system.Status.GetErrorText(sc)
set sc = ##class(Ens.Director).StartProduction("GOJ.IrisApp.ProductionDev")
write $system.Status.GetErrorText(sc)

HS.SDA3.Container is a registered object and not a persistent one, so you can't pass it directly.

What you can do, however, is to pass existing stream id in your request, this way stream is not copied twice (you only pass an id) and receiver then can recreate the same HS.SDA3.Container from a stream.

Try these tutorials.

Consider using Angular with InterSystems IRIS REST APIs.