I am new to Portable Apps and need guidance as to which apps are the most important to make the application functional

This depends on what apps you need.
I would try a browser (Firefox or Chrome), a writing programm (Abiword is smaller but LibreOffice can do more), Sumatra or Foxit to read pdfs and VLC or Coolplayer for playing music. And some games or something from the education section if you want.

The good thing with portable apps is that unlike normal programms where uninstallig can be a bit of a hassle, with portable apps, its easy: Just uninstall them using the Menu or delete the apps folder (X:/PortableApps/WhateverApp).