What kind of hardware would be necessary for my purposes?

- 4k (if I get it then 8K) video editing

- Minecraft with texture packs, mods etc etc

-GTA 5, later then GTA 6 when it's outside

- Twitch streaming

And what would that cost?

In any case, you need a very powerful graphics card, which is currently extremely expensive.

With 4k I would recommend 32gb 3600mhz Ram, 8c / 16t processor and iwas around ne 3070. Price around 1500 euro-2000 euro. If it is only a matter of cutting and not recording with the PC, a significantly poorer graphics card is sufficient. But if you also want to play games like cyberpunk, definitely take a new generation graphics card. From Nvidia I would still recommend the 3070, from AMD the 6800xt. But if you are currently looking at the graphics card market, find a graphics card that fits your overall budget and wait until the market returns to normal.

Hmm it would depend on where you buy it I would now estimate around 1600-1800 euro but it could also be more or a little less

It's best to just take a look at the finished PC pages because they have the statistics and then you see how well it fits you, then order the parts yourself and then assemble it

Should the games also run in 4k?

If not, then I would simply put a system with a GTX 1660 super or an RTX 2060 combined with e.g. An Intel Core i7 10700K and 32GB RAM in the room.

If 4k gaming is also planned, an RTX 3070 or something will probably have to go in. However, this makes it difficult for prices below 1500 euro.

For 8K video editing, only high end comes into question. A gaming PC is no longer enough, a workstation is needed.

Times as a rough direction.

Ryzen 9 5950X
At least 64GB RAM, more like 128GB
Nvidia RTX 3090

You are there with several thousand euro.

If you limit yourself to 4K, the whole thing will be much cheaper.

If you look at the current hardware prices, you won't get very far with 1.6k to 1.8k. An RTX 3060 alone currently costs 1000 euro. If all the rest of the rest is added, it should cost at least 3k.