I did some more stuff with my Doom 2 map yesterday. First, in UDB, I changed the textures in the starting room of the map, which hopefully looks a little better now. Though, I also went back to Slade and added a UMAPINFO lump to the WAD file. I changed the name of the first map from the default "Entryway" to "ArtistPanda5 Test Map" (I'm not very creative), and also added an intermission screen with some text (not the regular "end level" screen, one that can be used to add story exposition) that will display after you complete the map, and before the Underhalls map starts.
The level name in the third screenshot might be a little harder to see, since for some reason it's displayed in a smaller font than normal in Woof!, at least for the custom level. It looked normal when I tested it in GZDoom.
Unfortunately, I don't have a screenshot of the intermission screen at the moment, and I can't take one for now, so I'll have to post one another time.
EDIT (11/14/2024): I took longer than I needed to, but here's a screenshot of the text intermission screen: