Thanks a lot for your time and explaining your question in a detailed manner.
Answer of Scenario #1
Your observation is correct. According to current logic, filtering is possible on the current active results. There are several reasons behind this logic, so it is currently not possible to remember the filtering for pagination.
Answer of Scenario #2
You are confusing one step only i.e. 3(a)
Choose Template = Portfolio Sortable 4 Column Template for both
It should be:
Choose Template = Full Width Widgetized Template
As you are expecting to use widgets, so it should be Widgetized Template instead of any other template. Full Width Widgetized Template is also a powerful feature of Contango Pro. You can design multiple layouts by assigning different widgets to this template.