To install locale, execute during docker build:

set sc = ##class(Config.NLS.Locales).Install("deuw")

Check this answer. And this article.

request should not contain process, there is a separate process variable for that.

Users certainly should not be able access Ens_Config.Credentials table, maybe some user has permissions too broad?

What you can do additionally is to store credentials in a separate SECONDARY database. When you create a new interoperability namespace (in non HS installs), it should be created automatically. Still, you can manually create this DB and related mappings by calling CreateNewDBForSecondary.

After creating secondary db, check that no one has R on DB resouce.

Additionally you can encrypt the db file.

Sure. There are two ways:

1. Switch to another namespace to execute your query:

/// Get a list of all mirrored databases as a $lb()
ClassMethod GetMirroredDBs() As %List
{
    new $namespace
    set $namespace = "%SYS"
    set sql = "SELECT LIST(Name) dbs FROM Config.Databases_MirrorDatabaseList()"
    set rs = ##class(%SQL.Statement).%ExecDirect(,sql)
    do rs.%Next()
    set dbs = $lfs(rs.dbs)
    kill rs
    quit dbs
}

Now you can have this method in USER namespace and it would automatically swith into %SYS, execute query, iterate over the results, write results into a local variable, switch back into USER namespace and return the value back to you.

The main thing you need to remember is that result set iteration MUST happen in a target namespace.

2. Map classes and globals to your namespace. Docs. Table would be available as if it was created in your original namespace.

Check the docs, specifically the target argument.

Say you have this query:

SELECT a, b, c
FROM mytable
WHERE d=1 AND e=2

If you want to change fields in SELECT or WHERE, you'll need to rewrite your query by adding or removing it's parts. Source control diff would also show a whole line change.

But if you write it like this:

SELECT 1
  , a 
  , b 
  , c
FROM mytable
WHERE 1=1
      AND d=1 
      AND e=2

You can comment out any field or condition simply by adding --:

SELECT 1
  --, a 
  , b 
  , c
FROM mytable
WHERE 1=1
      --AND d=1 
      AND e=2

when you have a lot of conditions and need to iterate fast, this way of writing queries is much better for debugging and source control since diff is always contianed to the one line you edit.

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.