Bro, you seem to be in a little over your head.
Any effect, anywhere and everywhere, is done in multiple layers. I've had single shots with upwards of 100 layers before compositing the effects.
Keying (or perferably a luma transfer setting like screen, add, etc) is pretty common and one way to composite in pre-rendered stuff. You can also render out with an alpha channel and go from there
Doing cinema effects in an NLE like Vegas is nuts. Download the trial of AE, spend every waking moment at Video copilot doing their tutorials (starting with the basics that if you've never opened AE before, you can get through it easy... 10 hours of free lessons for
basics, over a 100 total) and go through it to learn the basics and a few more advanced techniques for effects.
It's not just about learning the exact effect he teaches, it's about the technique so that when you sit down and say "i need a ray gun" you have some ideas on steps of how to achieve it.
Or, if you're insanely anti-after effects, go the Blender route and learn 3D from the ground up 100% free.
I keep mentioning free because you've made it clear that times are tough and I can appreciate that, but again, this is all FREE and PROFESSIONAL.