Doorstopper :
Yeah I actually will be using an old seagate drive that I picked up from a local refurbished pc parts store just for all my back ups, movies, music, and such... I know it's not the most ideal solution, but it was only $75 for an old 5900rpm 2tb hdd.
As for MLC, TLC, and SLC... I have no idea what the difference is, and my phone won't let me open the links you posted.
Hm ... not that bad ... I have the 256gb 850Pro as on OS drive and have on it a work partition in case I need to work on some heavy image or 3d modelling files, the rest is all stored and accessed from a 1tb sata-II 3Gb/s 5400rpm internal hdd. With this config, and staying away from bloatjunk, things run pretty fast, so in your case, though you are right in saying that it isn't the best scenario, I'd say it's pretty good. Besides, SSDs are not for storing data, HDDs are for that so I think you've done the right choice.
As to the vids - It's YV vids so dunno why u cant see em, but the 3 terms are just the technology used - SLC - single level cell or 1 bit per cell - 2 logic states 1/0, MLC - multi level cell i.e. 2 bit per cell, 4 logic states 1/0 1/1 0/0 0/1 and TLC - 3 bits per cell - 8 logic states ... you can figure em out. The technology has evolved nowadays and tlc is more durable now but SLC would be preferable, though there are tradeoffs and caveats. Also, data is easier to read from SLC than it is from a TLC. That said, I'm not 100% convinced how much the real performance and durability difference is btwn modern day SLC vs TLC but it requires some googling and figuring out. This might help -
http://www.kingston.com/us/community/ArticleDetail/ArticleId/12?Article-Title=NAND-Flash-Technology-and-Solid-State-Drives-SSDs
As to your choice of producer - I'd stay away from Samsung, though I own 1. I think their SSDs are ok price-wise and even performance-wise, but beware of what happened a year or 2 ago when Samsung killed half the worlds 850Pro's with the way their non-magical Magician pushed the then 02 firmware upgrade. Need I mention what is happening nowadays with their flagship phones? So ... yes, competitive price they do offer, but that clearly comes at the cost of some corner-cutting here and there as you can see. When I was looking for an ssd and landed on the 850Pro 2 years ago - a real competitor for it was the SanDisk Extreme PRO https://www.sandisk.com/home/ssd/extreme-pro-ssd. SanDisk have prolly introduced even better ssds by now. Also, their price was similar to Samsungs price back then so ... take your pick. If I could rewind I'd prolly go with SanDisk.