Thanks to Jim's brilliant suggestion about how to create media layer where I don't have to hold keys down (simply creating a whole new layout where the media keys are on the main layer, then have it in a jump location for quick switching), I've finally created something that seems to work, but I have more to figure out.
Had some trouble though. First I created the new layout and put it in a jump slot. That was already assigned to the iphone so I changed some settings to make it for the Mac. Then I tried to pair it to my Mac and had a lot of trouble. I did unpair it from the phone, but I could not get it connected to the Mac. Sometimes it would say, "connected", but nothing seemed to work. I had a hunch that maybe the editing I did to make it do media was the problem because I had removed all the alpha characters and, in some of them, put media control in. Even though I didn't change any green layer stuff, where the numbers are, I thought maybe editing it kept the codes from number code from working (I tried both without holding down space and with it with no luck a bunch of times)3
So I went back to another layout that worked and installed it into that slot (I'd edit it after pairing). Still had trouble! Eventually it worked, but darn if I know what I finally did that made it work. Then I started editing.
Basically I put the stuff from the media layer onto the main alpha layer. One issue there was that there is a "beginning of track" command on the media layer, but I couldn't find that in the list of customization commands so, for now, I don't have that.
Then I started thinking that wouldn't it be a good idea to still have access to alpha characters even on this customized layout. So I went to Number Lock and entered all the main alpha layer stuff there (so no number pad in this setup). Seems to work - upper and lower case. Only thing I'm missing at the moment is numbers on that layer but I haven't had time to go further. I assume it won't be a problem to add them across the top by pressing space.
Since, when typing, there will be more constant activity than when using media, the Number Lock timeout of a couple minutes shouldn't be a problem and I won't have to jump back and forth a lot. Just do the lock.
Just added the numbers and other normal green layer stuff onto the Number Lock green layer. Seems to work fine!