Apple’s daap client (iTunes) is crippled in a number of respects with regard to what it can do with remote files. Songs that are shared by another iTunes client can’t be burned to cd, arranged in playlists, etc. So that part has to do with iTunes, not mt-daapd.
As far as the playlists go, between november and january (ish) playlists haven’t worked on nightlies. Since Januaryish, though, they do, but now they are edited via the web interface instead of in a file, having the advantage that they take effect immediately (without having to restart the server). You’ll want to take a look at the notes on the nightlies page, as that’s pretty much the only place the smart playlist language is documented, although there is a wizardy thing to help build playlists.
It will read standard m3u files, though, too, so if you have those it should work.
Is your music library a mirror of an iTunes library? If so, then by copying your iTunes Music Library.xml file into the top of the mp3_dir, mt-daapd will read your playlist info from itunes.
I’m not sure if that answers all your questions, but ask again if I’m not clear.