At some point Andy says, "I have lived and breathed radio since I was a little boy. I've done just about every job you can do at a radio station." So the song is definitely about Andy and not Johnny. The very first episode is Andy arriving at WKRP and finding out he might not be staying before this pilot even ends.
"'Extremely High Voltage.' Well, I don't need safety gloves, because I'm Homer SimpsonzzzZZZsssSSSbzzz" - Frank Grimes

it was about Andy, but truly about all the dj's of the 70's and 80's who moved from town to town.
Check out the Harry Chapin song "WOLD".

It could possibly be just as you stated. Definitely plausible. He did mention in Les' Groupie, though, when they were talking about weird fans, that a female listener wanted to wear his clothes or try on his clothes or something. So it could be that at one time he was actually a DJ and then moved into programming.

Good points, lol.
Sort of like "lending an ear" when a person wants someone to listen?

If it was supposed to be Andy, why would it say "living on the air"? He was never on the air.
That's the metaphor. You are correct that Andy was not actually an on-air personality. However, the business he's in is to put programming on the air, so he is "living on the air" in a figurative, not literal, sense.
If you asked if I could "lend you a hand," my hand could be helping you, but it would need the rest of me to make that happen, and it might not even be my hand that is providing the help. And I'm certainly not detaching my hand to give to you as I might "lend" you my hammer, my book, and whatnot!
And just to have even more fun here, even if it were Johnny or another on-air personality, they are "living" on the air only temporarily as part of the jobthey do not actually reside "on the air." And radio waves are only "on the air" in that they move through the air from transmitter to receiver.
"The past is never dead. It isn't even past." William Faulkner

I have no idea. I don't remember hearing that on the show.

Didn't Andy work as a DJ before shifting into programming work?

If it was supposed to be Andy, why would it say "living on the air"? He was never on the air.
On a side note, when I saw this show as a kid, I did think it was about Johnny. But I thought the line was "up and down the aisle", as if Johnny had been married and divorced a few times.

Oh, I haven't seen that episode yet.
I use to see the show as centered around Johnny but seeing them now, it looks like no one is the main character.

It's definitely about Andy, who was supposed to be the primary character on the show when it started. In one of the episodes he talked about his life, using the line "town to town, up and down the dial" which got a laugh from the studio audience.

I always sort of got the impression it was more about Andy Travis.
I can only conclude I'm paying off karma at a vastly accelerated rate.