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A whole lotta text but I would question some things you say;
Case: 800D is a great case but probably wayyy too big (and expensive) for the purpose here. If you're gonna pack a ton of hardware and stuff into it, sure go ahead, but otherwise just save some money and get a nice mid-tower case from brands like NZXT, Corsair, etc.. I wouldn't recommend cheaping out on the case but no need to go overkill either. $75-100 ish is usually a good price range for a case that is good enough.
Also, I most certainly hope your 800D is not made out of actual iron because that'd rust and be pretty bad for several components. Not sure where you read that but steel and aluminum are the metals almost all cases use, not iron.
Power Supply: Indeed, don't cheap out here. Get a good power supply from a good manufacturer (Corsair, Seasonic, NZXT, Cooler Master etc.) and be sure to get something with at least 80 plus bronze. (Stuff like 85 plus or 90 plus is not official; 80 plus is the only official rating system with various metals to refer to the grades). For wattage, 600-650w should be plenty, higher won't damage anything but it won't make any real difference either.
CPU: As has been said, i5 should be enough on the Intel side, otherwise keep an eye on what'll happen with AMD Ryzen which should be out around March.
RAM: Yep, RAM is cheap and 16GB will be more than enough. The dual/quad channel thing is kinda irrelevant here so no need to bother too much with that; Just buy whatever cheapest. 2x8GB is generally easier too because it leaves you the ability to add more in the future should you ever wish.
Motherboard: The essentials have more or less already been explained here. Everything else is nice to know indeed with the different sizes but rather irrelevant so long your case can support it.
Graphics Card: Yep, pretty much what was said. Look up reviews and take your pick depending on what fits your budget best. The graphics card should take up the majority of your budget though (you optimally wanna get the best one you can afford). Again also keep in mind AMD should release new graphics cards very soon too.
Hard drive: Honestly, whilst I agree SSD makes a huge difference and it is quite a night/day difference, I wouldn't say it's completely essential. You
can make due without one though it is recommended you indeed put in an at least 240GB model if you can afford one. But it''s not the end of the world if you decide to skip it for the time being.