Music services/storing music

I have yet to download any music from the iTunes store, but want to start.
I see Amazon has an MP3 download site also. Can these be stored in iTunes?
I have music stored on a an ext. hard drive. Some downloaded from the internet, some copies of certain tracks from my CDs. I'd like to move these song tracks to my iCloud on my iMac so I can access them on my iPad. Not sure how to do it.
Should these be moved to my iTunes library (which is currently empty) first and then they wilI be automatically sent to my iCloud (I think)?
Is the iTunes library the best place to store my other music?
Will iTunes mess up my songs that were not downloaded from iTunes?
Can my music be stored in MUSIC under the finders menu?
This is all probably something you all understand, but I grew up when typewriters and vinyl were the standards. Also learned my electronics on vacuum tubes.

Only because it's easier, I'm going to do this one at a time.

Bill Gates Jr. said:

I have yet to download any music from the iTunes store, but want to start.
I see Amazon has an MP3 download site also. Can these be stored in iTunes?

Click to expand...

If the files don't have DRM, iTunes can play it.

Bill Gates Jr. said:

I have music stored on a an ext. hard drive. Some downloaded from the internet, some copies of certain tracks from my CDs. I'd like to move these song tracks to my iCloud on my iMac so I can access them on my iPad. Not sure how to do it.

Click to expand...

You have two options here. First, you can simply sync your iTunes library with your iPad. Or, you can use iCloud Music Library which is part of Apple Music. You can get Apple Music for free for now and, if you like it, you can continue to use it. That said, other services such as Google Play Music and Xbox Music are free and do exactly this - act as services to stream your own music everywhere.

Bill Gates Jr. said:

Should these be moved to my iTunes library (which is currently empty) first and then they wilI be automatically sent to my iCloud (I think)?

Click to expand...

If you have Apple Music, yes, the songs will be uploaded. See here for more info.

Bill Gates Jr. said:

Is the iTunes library the best place to store my other music?

Click to expand...

That would be a personal preference.

Bill Gates Jr. said:

Will iTunes mess up my songs that were not downloaded from iTunes?

Click to expand...

Mess up how? It won't threaten the integrity of the songs if that's a concern.

Bill Gates Jr. said:

Can my music be stored in MUSIC under the finders menu?

Click to expand...

iTunes ultimately stores it here. Otherwise, it's a folder like any other.