stefanDB

there is also a 4+4 pin connector, that one is different, but all PCIe power connectors are 6+2, you never see ones that are only 8 pins

that will be fine, way below 10A.

true, as long as the current isn't over 10A, which it probably won't be unless you have a huge mining rig or something

if you want to get the best performance for your money, just buy a 1080. I don't think you really need to upgrade the rest of your components, although you could if you want better looks and slightly better CPU performance for example.

I think you would have to uninstall the drivers and install new ones.

as long as you don't use a conductive paste you can safely use too much. Make sure all the corners of the die are covered because there is no IHS on a GPU

Only apply to the die. Other than that, as long as the die is completely covered, you're fine. 
 
Because it's a gpu, the spread might be a little weird, so make sure you get the corners too, because it looks like the corners of the die in the first pic wasn't covered completely. 

that is indeed an RGB cable, and it should go on the RGB header on your motherboard, if it has one. The cable has a ground, green, red and blue cable as you can see on the side of it. 

PCs like that one often come in different varieties, they may have different PSUs and I wasn't able to find any info on it in my 2 min search. it is far easier to just unscrew the sidepanel and take a look, he doesn't need to take apart the actual PC components. I also recommend a blower style card since there only seems to be one tiny exhaust fan, and overclocking the card isn't great anyway due to the PSU.

try to boot the PC with as few components as possible, so only 1 RAM stick and no peripherals, HDDs or such

try changing the resolution in windows instead of nvidia control panel

Definitely go with the 8700K

It is easier for the people here to help you if you give a link to a PCpartpicker list, just to give some advice

nice might want a ssd though and maybe a 500 watt supply for a bit of upgradablity if possible

your post is kind of weird, pls edit that stuff out. 
Also, at this point in time I really don't recommend buying last gen intel CPUs, especially not the i5. get ryzen or 8th gen intel.
I don't know how good seasonic is at making PSUs, there is a list of how good/bad PSUs are somewhere on this forum, you should check it out.

if you could find 3000MHz RAM that would be nice, but only if the difference in price is small. Do pick a decent brand though, ryzen can be a little difficult with RAM (g.skill is fine, corsair is also very good)

Then you need a 1080 lol 
 
just get get the best you can for your budget. It’s budgest that defines what you can do not what you want to do 

If he's not telling you the brand or its unbranded, don't power a 1070 with it.

you litterally said that you don't know much about PCs, but then you don't listen when people who give you advise. I know you are going to be mad at me for saying this, but if you don't listen to the advice of those who probably know more about PCs then you, you will end up with a worse PC for the budget. and if you only use the PC for games, then it is kind of a waste of money to buy a six core CPU.

if you are building a gaming PC, then I would go for the sata one as the extra speed won't make a huge difference but the extra storage will.

if you are building a gaming PC, then I would go for the sata one as the extra speed won't make a huge difference but the extra storage will.

if you are building a gaming PC, then I would go for the sata one as the extra speed won't make a huge difference but the extra storage will.

if you are building a gaming PC, then I would go for the sata one as the extra speed won't make a huge difference but the extra storage will.

if you are building a gaming PC, then I would go for the sata one as the extra speed won't make a huge difference but the extra storage will.

There isn't much difference, honestly. But generally speaking, if there is an object that blocks or partially blocks "the way" for air in or out (even dust trays) you want to push air stronger instead of having more air flowing.