Just some important stuff for starters

I'll cut to the chase, when adding override mats to a model you're met with its...well...mats, there's a couple things you can do to affect them with, such as but not limited to:

$Color / $Color2: These parameters are primarily used to tint or change the color of a material. (vector3)
$BaseTexture: Allows you to replace the original texture of a material with a new one, enabling you to change its base color.(string)
$PhongBoost: This parameter can be used to add glossiness to a texture and is related to how the material interacts with light.(vector3)
$SelfIllumtint: This parameter makes a material glow, creating a self-illuminated effect.(vector3)
$Alpha: Makes a model or element visible(1) or invisible(0).(float)

These are the basic ones, for alpha you can create an AS(Animation Set) from an the element(with OverMats), tho to see it make sure you SWITCH OFF SCENE HIERARCHY

When using $color / $color2 or $selfillumtint you have to use RBG. INTERESTING FACT, if you find a color you want and have the RGB code for it, to get it into SFM you have to use this formula:

(R, G, B)/255

since SFM uses 1 as full color and 0 and none the basic colors are:

Mains -- Red (1 0 0), Green (0 1 0), Blue(0 0 1)
Combos -- Purple(1 0 1), Yellow(1 1 0), Teal(0 1 1), Pink(1 0.1 1

When keyframing or "adding a bookmark" in the animation strip, not the motion one idiot, sometimes you can get what's I call a FRAME TANGLE where movements of your model is recorded without a keyframe and it lowk makes your model bug out. To fix this, add a bookmark WAYY BEFORE the "tangle" or unkeyed movements, and add a frame RIGHT AFTER the "tangle" delete the before bookmark first, then the after bookmark. If it doesnt work, do the steps again but remove the after bookmark first

It was very tricky for me to find reasonable ways to do these, but I found the best if not ways to do em

For custom sound files:
https://audio.online-convert.com/convert-to-wav
Make sure file is 16-bit atleast, 22050k audio sample rate
Format/rename the converted file[s] as " WAV -- 'file name alr there' "

For custom texture (.vtf) files:
Use $basetexture in SFM
Use 'models\'custom-filename'\'custom-vtf-name' (ex. for me it's models\spacesvtfs\'custom-vtf-name')
You'll need VTFedit to make and save textures but hahha i can't help you with that have your own fight