Single player, by 
Using a layout you're familiar with is a smart way to get used to a new editing tool! One thing you can try next is changing layer sizes and other layer properties, so the background sky can be the right size. You can press Ctrl+8 to edit layer 8's properties, for example. Another good thing to focus on is making sure you're using tiles that look right next to each other… most walls should look a little different on the sides than on the middle. But you've figured out how to place events and that's a good step, and the big carrots look great. I'd recommend looking through this site: https://www.ninjadodo.net/htjcs/
Also, this is a good source for JJ1 music, they're directly converted from the original files and have a much smaller filesize than mp3 versions: https://www.jazz2online.com/downloads/3151/jj1-music-pack/