Ok, I'll google Ladix's MPQ thing.

Now about the second, I understand I need to place .blp in baked textures file so the game can load up said texture, but I don't know where those directories are in my computer.

For instance, for the dbc files, there was a folder in MANGOS called dbc, where (I assume) you're supposed to put them (the DBC files), so I did. But I have no idea where the folder I'm supposed to place the blp file is, what its name is, or how I can access it.

This should be what you are looking for. Although it wasn't that hard to find. The Tutorial Sections aren't that full.

Edit:
This does not use custom models though, but I think you don't mean it that way anyway.

I've tried to use that tutorial, but I've run into a problem: when the author says export your model as 3dS, I do, but it doesn't create any additional .tga file to edit. When I export it in its standard format, it does create a .tga which I then convert into .png format, but when I drag that file over the BLPConverter to convert into blp format, nothing happens, the screen just flashes for a milesecond and then nothing... no new blp file, nothing.

Now, I don't know if this is relevant but I'm using a really REALLY old version of WoWModelViewer (0.5.08) because I'm still working in version 2.4.3 of WoW, and that's the only version of ModelViewer I could find that was compatible with it. If that's the problem, I'll update.

Please help me solve this! I've dreamt for years of creating my own WoW experience, but I can't overcome these barriers on my own, and I'd hate to have to give up on my dream.