I wanna make a Doom mod with a Friend

As the title suggests, I wanna make a doom mod at some point with my friend, this of course being a major task for someone like me who's yet to actually mod a game.
I know I should probably start small, and I am unsure which software I should use to work towards this goal. I've been using DeePSea up to this point and it worked just fine, but I can't help but feel it, dated to put it in a way? Other software I found no longer had links or otherwise so it was my only option. On top of that, the tutorials stopped working in it, and frankly I'm really confused without it lol. I know I shouldn't just jump straight into it so I wanna try and learn what I need up til the actual time to make said mod.
So my questions are this:
What software should I use to achieve this? Is there a more modern system people use to make mods I don't know about? And where should I start to head towards my goal?
I'm open to any and all suggestions from y'all, and I hope I get some much needed answers, thanks in advance

For mapping, use Ultimate Doom Builder. For other editing of WADs (i.e. changing music, adding sprites), use SLADE. Both are easy enough to use, but if needed you can ask around in the Editing Questions forum for tips and info on how to fix issues. There are also a lot of tutorials on YouTube as well as this very forum (Editing Tutorials).