First I just want to express how much I appreciate the replies, they have been very informative, and I have already learned quite a few thing about the game that I did not know.
Some mods that I have installed do not have NPC support, which I'm guessing are the ones I have to use the model_default command for, as I do have some skins that will allow me to just use the name with no issue.
Although I do have quite a few free keys, your suggestion of a menu is very interesting.
I've been essentially playing this game as a sandbox lately, I'm really only using Movie Duels as a base because it comes with tons of maps, character models, music, and a lot of gameplay tweaks I like, and I've just been piling maps and playermodels on top, just to mess around with (duel, take screenshots, essentially Star Wars GMod) so as far as cutscenes, I don't really think I'll have any issues.
Movie Duels actually has something similar to your ingame menu mod, and some of my skins do show up there, however many do not.
I think the reason is probably because a lot of my skins are old, and come from mrwonko.de, which are very barebones mods.
I'm really looking to learn as much about this game as I can!