What is the effect of heat on vegetable oil?
Upon heating, vegetable oil will first become less viscous (less
thick and more runny) as it is heated, and eventually, if heated
hot enough it will smoke and then burn.
No, it's primarily the heat, heat distribution and quality of the popcorn that affects how much of it pops. The only effect that it might have is if you use an oil with a low smoking point (like butter) it might not get hot enough to pop all the kernels before it burns. That's why vegetable oil is better for popping and melted butter is added later.
Vegetable fat (or vegetable oil) is normally a mixture of corn oil and/or rapeseed oil. To produce your own oil at home (from any crop) is quite an industrial process, involving grinding up the kernels and then pressing them at very high pressure (sometimes with added heat). It's not something most people would attempt to do.