First of all, about your code.
As I see, you are copying data from one customer to the same customer (the same situation for product). So you don't have to choose these chars as "Fields to be changed", coz these fields doesn't changed. You could leave them unselected. Then all your data will be splited into several packages with similar values of unselected fields. In each package there will be new rows with new values of "fields to be changed".
Q2. Frankly speaking, I don't understand you. 
But IMHO one MultiProvider with all necessary cubes is a good solution.
Q3. It depends on interface you use. But everwhere there is an message area. Place it in your layout and you'll get message something like "Function F1 finished succesfully".
Here is place where you could finf in WAD:
Unfortunately I have only Russian interface. It is Extended group and System messages object. Or something like this. I'm not sure about translation. In BEx just choose object whith the same icon.
By the way, don't forget to switch on messages in Layout params:
So choose Web-Template, and turn on first two options.
I hope it will help you.