After updating to latest, or restore, I noticed that All of my music on iPod was gone.
If you did a Restore on the iPod, that erases the iPod and installs the latest version of iPod's software. If you did an Update, that should only update iPod's software. Doing a Restore actually works out fine, because your iPod was probably formatted for Windows; it's better for it to be formatted for Mac, since you are using it with a Mac going forward. Doing a Restore using iTunes on your Mac re-formats it for Mac.
This was music that I downloaded from my CD's to my iPod...
The songs on the old PC do not need to be purchased items from the iTunes Store. They can be from ANY source, as long as they are song files that iTunes can play (or song files that iTunes can convert into a compatible format while importing).
I took an external flash drive and copy & pasted to it.
To add your song files that are on your USB flash drive an iTunes library your Mac, you can do it one of two ways. But first, open iTunes preferences Advanced pane (on the Mac). There are two checkboxes there for Keep iTunes Media folder organized and Copy files to iTunes Media folder when adding to library. You should checkmark both of those boxes, if they are not already. For a Mac, those two settings are enabled by default (unless you changed them). At the top of that Advanced preference pane, it shows the path to your iTunes Media folder. You don't need to change that path, but (as an FYI) that is where iTunes stores your song files.
The two ways are (1) to transfer your complete iTunes library from the old PC to the new Mac OR (2) to only transfer your song files from the old PC and add them to a new iTunes library on the Mac. The difference is that with (1), you get to keep supporting data such as playlists, ratings, play count, date added, etc. It will be the same iTunes library on the new Mac. With (2), the iTunes library on the Mac is new, and you are adding your old song files to it.
You still have your old PC with your old iTunes library still working, so you can use either method. It sounds like you are more prepared to use method (2), with your song files already copied to a USB flash drive. Do you want to continue with that method, or go back to your old PC to transfer the complete iTunes library, which is method (1)?
