Best hard drive setup for animation videos?

Hi. I am self-taught at many of the Adobe programs and I know them pretty well, working in a low level professional design capacity. I have probably read a hundred threads and watched dozens of videos on what I'm asking but I'm still unclear as there seems to be conflicting options on a few things:

I make short animated videos. They can last anywhere from 1 minute to 30 mins. They are typically made up of the following: complex Illustrator and Photoshop files which are then brought into After Effects and animated. After that they are exported to .h264 files which are imported into Premiere. In Premiere they are combined with AVCHD video files and WAV audio files. I typically use Dynamic Link to make further edits to the video in AE and to add titles/effects/etc. Then I export an .h264 file using Media Encoder.

I am working on a 2012 Macbook Pro running CC2017 and OSX Sierra. It has two USB ports and one Thunderbolt port. I am currently running everything off my internal C drive and when at home I keep it plugged into a Thunderbolt port and backing up via Time Machine to a USB hard drive. The CPU is 2.9GHz Intel Core i7 and the graphics is stock Intel HD Graphics 4000 1536MB, and the computer has a 1TB 7200RPM drive with 500GB filled and I've upgraded the memory to 16GB.

I have been doing this for long time and I know that there are better ways to setup my system. My main concerns are the amount of time it takes to export files and that After Effects is so slow to preview everything and seems to reload everything each time that I make the smallest change. I understand that there are ways to speed that up but I'm wondering what my best path is considering monetary limitations etc.

My current plan and questions:

I understand that things such as project files, source media, scratch disks, caches, auto saves, and exports should all ideally be on separate hard drives, but since that's not realistic I'm wondering what the best setup is. I have read the generic setup post in the hardware forum among many others, but I'm still confused as to best practices. As I see it there are three factors: portability, redundancy, and performance. So,

- Is running everything off of my C drive shortening the life of my computer?

- I understand that there is a performance advantage to storing some files on external hard drives when working, but at what point does that reach the point of diminishing returns? In my experience transferring large folders from my C drive to an external drive it takes a long time, I don't understand how constantly moving things from one drive to another doesn't result in SLOWER performance. If I had three external hard drives plugged into my computer wouldn't that slow things down significantly and counter act any speed increases? Or am I just not understanding how computers work?

- Would it be better to invest in an external graphics card than several external hard drives?

- As I understand it, every time I try to play a preview of my composition in After Effects it takes time to load because it has to queue up a preview, which I have to wait to load into the RAM in order to watch it. I read that I should save my After Effects cache on an external disc in order for AE to save the preview that it just played so that I can make small adjustments and it won't take so long to queue up a preview each time. Why does it load up into the RAM now? Isn't the RAM needed for other things? Why can't I just point the cache to my C drive?

- For the type of work I'm describing, would a solid state drive be better than a thunderbolt drive, or would it be the other way around?

- Is it also better to be working off external hard drives for Illustrator and Photoshop work?

- Is it much more important to work off of a powered external drive instead of a usb powered external drive?

Thanks for any advice you can offer.