First things first, dump all those files in a folder that's named something you'll remember. When you try to change the tones, it's a lot easier to do it if you use an aftermarket txt app like go SMS. If you do, it will ask which app to use.... Choose the aftermarket app, then 'music'; all the tones you've added will show up. But yes, plug your phone into your pi and drag and drop. You'll need to rescan media, but rebooting does that for you.
Now it plays the entire file, so I make ringtones 30 sec, since that how long 5 rings takes. For txt notification, I use short tones, like Peter Griffin from family guy saying "who is this?" that's actually my most used one.