I wouldn't go as far as to say that Slade was
necessary for those things. Given that most lumps can be edited with text editors, or graphics editors (which IzaiahConn may already have personal preferences for) and thrown into a zip/pk3, and textures can just be put into a textures folder in the zip and work as well.
Don't get me wrong. I'm not saying that Slade isn't useful - it is. It's very good for setting sprite offsets, doing colour translation and palette related stuff, working with the PNAMES, TEXTURE1 and TEXTURES lumps, handling lumps inside WAD files and so on. It has many uses, and it's good at them. I use it all the time. So, I'm not saying it's not a useful tool by any means. I'm just sating that it isn't an absolutely essential one and it might not be something that someone needs when setting out to make their first mod. Sooner or later though, they may well want to use it.
I've also noticed that it isn't unusual for an inexperienced modder to make PK3s with odd internal structures, repeated lumps and strange marker files that make the files difficult to read (especially problematic when someone trying to help them reads their file with their own utils). It's my pet theory that these files are sometimes the result of a modder not entirely knowing what they are doing, using Slade and feeling their way while making mistakes along the way - not fatal mistakes, not "bad format" mistakes. Indeed, the modder often confirms as much at some point if they are posting about trying to debug something in their mod. Slade is quite a technical tool and it's quite easy to make messy file with it (which may, or may not, still be functional) if you are unsure what you are doing.
Of course, if IzaiahConn wants to make a totally WAD-based mod (i.e. more than just the map file(s)), rather than a PK3 one, then a tool for handling WAD files will be far more important and Slade would be the tool of choice for most people.
If you do have additional resources in your mod, I sometimes find that a good way is to simply use a folder. Inside the folder are other folders with the correct structure for a PK3 file and I just dump all the resource files into those folders. This makes it nice, quick and easy to browse and open any files simply by using Windows explorer. Both GZDoom and UDB can open folders like this and use them just as if they were PK3 files too. When I'm done, the structure is already there and I can just zip up the contents of the folder, rename ZIP to the accursed PK3 extension and I'm done.
https://zdoom.org/wiki/Using_ZIPs_as_WAD_replacement