I've been trying to figure out how to create a "CUSTOM" display toggle for a Window which appears when, toggle is selected? Anyone which can help me, would be a great help.

It's pretty simple to do. You simply need to use the "ident=xxxxx"
in the panel.cfg Windowxx section for the window you want to
toggle and have a custom icon to do the toggling.
Here's a sample of XML code to toggle a window with an ID of 10032:
Toggle Custom Window
10032 (>K:PANEL_ID_TOGGLE)
The BMP is the Icon bitmap. You can easily create custom bitmaps
using Paintshop Pro and similar programs.
Here's the first part of the Window specification from a panel.cfg
file:
[Window14]
Background_color=0,0,0
size_mm=1024,768
position=7
visible=0
ident=10032 <---------- this is what you use to create custom windows. Some Idents are predefined by MSFS but
generally numbers above 10000 can be used at will.
You also need to call out the Icon gauge on your main panel.
I put my custom Icons into a folder "PDS_Icons". It contains
the XML file and the BMP file. It can be located in your main
Gauge folder of the panel folder where you are actually using
the custom icon.
I added this line to my panel.cfg to place the icon in the
lower left area of the panel.
gauge85=PDS_Icons!Panel_32_Icon, 5, 740, 20, 20
If the new window covers up the main window, you will also need
to place the toggle window icon on your custom window so you
can switch back. Simply add the same line as above with the
appropriate Gaugexx= number.
Paul