thought I'd try to copy some MP3s up to the Central instead of ripping a CD directly in the Central.

It's interesting you'd try to do it that way just as a lark... I've gone to a lot of trouble to try to avoid ripping on my PC, because dropping a disc into the Jupe is so much easier.

I ended up with all the desired files in the new playlist and then dragged them down to the Artists section, renamed them, etc.

If the MP3s on your computer are already properly tagged, you don't need to do this step. Emplode will go by the tags embedded in the MP3 files. More information about tagging is here.

right clicked on them a few at a time, then used the Paste command in Emplode to plunk the files down in the Playlist.

As Roger said, you need to get familiar with your new friend, Drag and Drop. More information here. One caveat: The information I'm linking here talks about Emplode as it relates to the Empeg Car player. It mentions heirarchical playlists (the ability to make sub-playlist trees beneath the parent playlists), a feature that is deliberately disabled in the Rio Central.