App Loader problems

I'd run npm test on your PC in your BangleApps repo and see if it throws up any suggestions - that tests your app JSON for common issues.

If the app works but the app loader doesn't, it's most likely something in apps.json. The launcher looks at a file called yourapp.info which is auto-generated from apps.json - so you could look at that from the IDE's storage window and see if you can see anything obviously wrong.

You could also stay connected with the IDE while starting the launcher and see if there's any error message shown.

the Desktop Launcher is one that I don't even see come up on the menu

Yes, that's expected. The Desktop Launcher is a new launcher rather than an app (widgets don't show in the launcher either), so to make it work ideally you remove your existing launcher app and then it should come up.