bring aiff files in Music folder to iTunes, play thru Airport Express

Greetings audiophiles in MAC community!

I bought an HD music album in AIFF-C which downloaded to my MUSIC folder. Each of the the 31 or so files can be played in iTunes by default just clicking on the name in the Music folder.

Now I want to make a playlist of all those files in my iTunes library--and bring them over to my iPhone next.

1st problem was I couldn't find the MUSIC folder on my iMac (I locate the individual song files with Search). Eventually I found it in my USER enclosing file. It wasn't obvious to look there but after a while I found it. Q1-Solved!

Q2. Next problem - how to copy the files into iTunes Library. Shouldn't that be simple?

Q3. Then I want to get all those lovely HD files into my iPhoneX and iPodTouch.

Q3: These files are 96kHz/24 bit. Once they are in my iPhone 10 and I play them through my good Stereo system (via Airport Express) will they lose much fidelity...or are files played as 96/24 through my iPhone?