[@BrokenPromise]Thank you for your kind words. Yeah, creating assets, rigging them, animating them, then rendering and adding sound effects, etc. can definitely amount to a herculean feat. Thankfully, for this animation, I went with eevee, so I didn't have to wait long for these 400~ frames to render. 

My computer specs are thus!
CPU: i5-9600k
GPU1: AMD RX 6700 XT
GPU2: NVIDIA GTX Titan X (2016 card, but works for the Optix denoising and offloading rendering)
RAM: 32 GB
VRAM: 24 GB (both cards added together)

I actually used the method you're describing above where you render only key frames, then add them back into Blender and space them out to re-render the middle frames, but I did this for the mouth animation and decided against using it, in the end. It was just simpler to my process to render the in-between frames because I wanted animation to be going on in the background, too.

This animation took me about 3 weeks of work between getting the intro set, the characters modeled/animated, the sound, etc. It could have taken longer, now that I think about it.

Do you have any projects you wouldn't mind sharing with me from your previous work? I'm curious what you're using Blender for.