1. I found _playlist.html, but I could not find playlist.html (neither in the AppData folder, nor in the Program Files folder).
That's to be expected. Unless you change the _playlist.html template to output a singular file instead of 27 files (playlistA.html - playlistZ.html and playlist0.html), you will not see a playlist.html file. The output filename in SAM is just the "base" filename.
i.e.: If output is set to playlist.html it will generate the aforementioned playlistA.html, if you set it to superduperplaylist.html it will generate superduperplaylistA.html and so forth.
Another example: If you put playlistA.html in the Output field, you will get playlistAA.html to playlistAZ.html and playlistA0.html
I used _playlist.html for both input and output. Is this OK? Should I use playlistA.html instead, since that's where you land if you click the Playlist & Requests link?
Nope, neither of that is correct. If you set the output to _playlist.html you will get _playlistA.html and will need to adjust all other files to be aware of the new naming scheme. The templates "as is" are meant to use _* files as input and matching names without underscore in front as output.
The HTML Output configuration for SAM should have ONE entry only in the Playlist HTML output section. It should refer to a _playlist.html file in the input file field and a playlist.html file in the output file field. (These files are generated and uploaded only if you explicitly tell SAM to do so)
There should be 2 entries in the General HTML output section (These files are generated and uploaded for every track played)
2. In the AppData folder, the _config.html file is blank, but the one in the Program Files folder has content. If I want to change the _config.html file (eg put in my email address), should I do that to the Program Files version, then drop that into the AppData folder? INSTALL.txt doesn't specify whether I should use the AppData folder or the the Program Files folder.
That's because the templates and instructions weren't updated for Windows Vista and newer.
You can't use the ones in Program files by default, because SAM can't write to that folder. (That is a security feature in Windows so Programs can't modify their own or other executable files)
You should only ever change files in the AppData folder (SAM refers to that as Data folder and userdir)