Workflow-ng is awesome. I just installed shipping price by amount myself without a problem. It is so simple and easy. I think workflow-ng is one the best thing that ubercart has.

Workflow-ng is like if this then this or else this and so on...

It has been only 2 days that I took ubercart and drupal (using both for the first time) seriously and I am pretty much satisfied that in such a short period I have learn and understood many things of ubercart and drupal. Great!

But I still don't have solution for questions asked above, expect the last one....