Best PC?

what will be the best gaming pc, price doesn't matter but preferablly minimal .

Well, if you're going to want the best gaming PC, the processor should be an Intel i7-7700k as it currently has the best ratings for the gaming portion. It has hyperthreading available since a lot of games require a single core or maybe two cores to be higher than the others. The AMD side, with the new Ryzen series, is great for the video editing portion as it has the best bang for your buck when using the processor amount and speeds.

For the video card, you will either want the GTX 1080 TI or you can also wait for AMD's new Vega release to see what may happen. It's supposedly competitive with the GTX 1080 TI. If it actually does, you can bet there will be a price war.

by the way

what is a difference between gaming and streaming?

since people usually use 2 computers.

@kaxap i guess you will need to run a hefty monitor with a high amount of pixels (e.g 4k monitor with good color accuracy), considering that you want the photograph to look like the photograph you are viewing. Therefore, you will firstly need a good amount of ram (32 gb), since some of the designer softwares might consume a lot, an SSD to render your work fast, and a good GPU and Processor to make the monitor run properly

This is true. I would, above all, recommend a good monitor with accurate color reproduction. This will allow you to get what you need for photography. (I also dabble in photography so I know the joys.) As for designing, I am going to assume Lightroom and such so you won't really need a GREAT GPU, but a higher end one would be nice.
According to the minimum specs of Lightroom, you'll need: "2 GB of dedicated VRAM is suggested for large, high-resolution (such as 4K and 5K) monitors."

Since you will want a 4K monitor, getting at least 3 GB will be preferable. You can do that at a relatively cheaper cost with the AMD 480/580. I wouldn't shell out for the NVIDIA's 1060 because FreeSync.

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Streaming is people who, typically but not always, game but also use their computer(s) to broadcast their computer to an online platform like Twitch. They need a CPU which requires more cores so I would recommend a Ryzen for that. The general consensus is i7-7700k just PURE gaming while Ryzen for streaming, video editing, and generally everything else since its performance/price is better.