Is there a way to know what index number of vertices I’m selecting with my mouse?
It seems so simple, so I really tried looking for hours, but I couldn’t find my answer.
A simple interface help or a python code, anything will be appreciated!
I don’t think you can assign numbers to vertices through the interface, so that would have to be coded.
there is a script that can show the index of vertices in viewport if you need to
but in the n panel you can see the location but not the index as such
see Crouch thread
and it is also included in the addons scripts
so just enable it and in n panel at bottom in display panel click on the index visualiser
and in the viewport in edit mode you’ll see all index as per n panel selection
salutations
Thank you so much! This was exactly what I was looking for 
I provided the said Crouch thread and his website link.
http://blenderartists.org/forum/showthread.php?t=149933
http://sites.google.com/site/bartiuscrouch/snippets