Better to use command JOB INT^SHUTDOWN instead of DO. When you use DO, the task will not be finished and will be marked as suspended, and you will have to resume it manually.

The example in the documentation to %XML.Reader, does not work for you?

    #include %occStatus
    // Create a new XML Reader class
    Set reader = ##class(%XML.Reader).%New()
    // Begin processing of the XML input
    Set sc=reader.OpenFile(filename)
    If $$$ISERR(sc) Do $system.OBJ.DisplayError(sc) Quit  
    // Associate a class name with the XML element name
    Do reader.Correlate("Person","Sample.Person")
    // read Sample.Person objects from xml file
    Set Count=0
    While reader.Next(.person,.sc) {
        Write person.Name_" imported.",!
        Set Count=Count+1
        Set sc=person.%Save()
        If $$$ISERR(sc) Do $system.OBJ.DisplayError(sc) Quit  
    }
    If $$$ISERR(sc) Do $system.OBJ.DisplayError(sc) Quit  
    Write Count_" Sample.Person instances found."

ROLLBACK should revert any changes in data which was done in a transaction, with some exceptions like $increment on Global.

You can look at this example.

Class User.Test Extends %Persistent
{

Property Name As %String;

Property CalcName As %String [ Calculated, SqlComputeCode = { set {*} = {Name} }, SqlComputed, SqlComputeOnChange = Name ];

Index ByName On CalcName;

Storage Default
{
<Data name="TestDefaultData">
<Value name="1">
<Value>%%CLASSNAME</Value>
</Value>
<Value name="2">
<Value>Name</Value>
</Value>
</Data>
<DataLocation>^User.TestD</DataLocation>
<DefaultData>TestDefaultData</DefaultData>
<IdLocation>^User.TestD</IdLocation>
<IndexLocation>^User.TestI</IndexLocation>
<StreamLocation>^User.TestS</StreamLocation>
<Type>%Storage.Persistent</Type>
}

}

Let's create first object

USER>s o=##class(Test).%New()

USER>set o.Name="testname"

USER>w o.%Save()
1

check saved in globals

USER>zw ^User.TestD,^User.TestI
^User.TestD=1
^User.TestD(1)=$lb("","testname")
^User.TestI("ByName"," TESTNAME",1)=""

and now open transaction, and do some changes.

USER>k

USER>TSTART

TL1:USER>set o=##class(Test).%OpenId(1)

TL1:USER>s o.Name="testname2"

TL1:USER>w o.%Save()
1
TL1:USER>zw ^User.TestD,^User.TestI
^User.TestD=1
^User.TestD(1)=$lb("","testname2")
^User.TestI("ByName"," TESTNAME2",1)=""

So, changes there, let's do rollback, and check data again.

TL1:USER>TROLLBACK

USER>zw ^User.TestD,^User.TestI
^User.TestD=1
^User.TestD(1)=$lb("","testname")
^User.TestI("ByName"," TESTNAME",1)=""

I think it will not be possible to restore backups from Caché/Ensemble to IRIS.

I'm sure that in most cases, it is possible to just rename CACHE.DAT to IRIS.DAT, and configure it exactly as it was in Ensemble, should work. And maybe it will work for you as well.

If you can easily repeat configuration on any just installed Ensemble server, do it in the same way for IRIS.

I think we don't have any other possibilities how to catch changes in source code. Do you know how to catch if any object in any class was changed, outside of this class, if you don't have any triggers there? No easy task. But I think it is possible to find some tricky ways if you don't care about just in time notifications. You can monitor any changes in the data, and filter by changing particular globals and subscripts. 

If you will describe what are you going to achieve exactly, it will be easier to help you.

Evgeny already mentioned just released preview version of IRIS 2018.2. And fortunately documentation from this version already available online,  and they offer to use new dialect  org.hibernate.dialect.InterSystemsIRISDialect. You can try to use it.

Very interesting question. Actually, it mostly depends on your application and how do you work with private data there. 

You can make application for any number of customers working in one database, with good security which does not allow to access data from one customer by another.  But in this case mostly means, that your application should be designed so, from the beginning.

Another and maybe simplest way is making separate databases for each customer. In Caché you can create multiple namespaces with different databases for each customer, but with the same database for a code of your application. So, you can update all sites at the same time.

Nowadays, I would recommend looking at containerization of application. And with kubernetes you can very fast deploy any new site with completely separate code and data between customers. But it means some work on how to prepare your application to be deployable with kubernetes.

%CacheObject was replaced with %Compiler.Type.Object. But this class was and still for internal use, how do you use it?

Silent install uses exactly the same manifest file, as for interactive. And it will install all components. But you can choose which one you really need with ISC_PACKAGE_CLIENT_COMPONENTS parameter and when this parameter empty will be installed all components.