Welcome to the forum!
Let's try to fix a problem at a time
, first the main WAD file problem, you mention you are typing the main wad folder, make sure that you only type something like C:\Doom2\ (i.e. without DOOM2.WAD) or it won't work. Also, make sure that all your wad files are located on this directory, or you will have to retype the directories for the different games main WAD files.
For using music packs and high resolutions textures, simply download the files and unzip them with their directory structures, they should work straight through
, make sure you enable high-res textures in the video options.
If you have further problems, please post them here.