Budget is around 2000 euros including monitor, keyboard, mouse, speakers and prices are still absurdly high in Europe. I want stability, reliability, best value for money, don't care at all about aesthetics, RGB shiny stuff, etc. Will overpay for some top tier parts like the PSU.
The heaviest game this will play for now is Witcher 3 1080p, I don't need more than 60fps for any game (no fps/racing/fast action, etc) so monitor will be 60Hz.

Case: Fractal Design Define R5 without window to keep it simple and quiet, it has 2 140mm fans, do I need more?
PSU: Seasonic Prime 650W 80+ Gold for peace of mind
CPU: AMD Ryzen R7 1700X or R5 1600X? I want higher clocks out of the box, maybe will do some streaming down the road, if I overclock at some point it will be only on air.
Cooler: have no idea, something from Noctua specially made for AM4 motherboards?
Motherboard: B350 or X370? I don't plan to Crossfire/SLI. Candidates for B350 are ASRock Fatal1ty AB350 Gaming K4, MSI Pro Carbon, Gigabyte GA-AB350M Gaming 3 and Asus Rog Strix B350-F Gaming. For X370, I don't know, there is an Aorus around 150 euros or the equivalents to the B350 motherboards.
GPU: RX 580 8GB or GTX 1060 6GB? For the first, Powercolor Red Devil or Sapphire Nitro+ around 300 euros, the XFX GTS is a bit cheaper, for the second MSI Gaming X 6G was my first choice but I'm not paying 350 euros for it, maybe Gigabyte Windforce at around 290 or EVGA FTW for 30 more?
RAM: 16GB (2x8GB) This is where it gets complicated. I've read that Ryzen takes advantage of faster memory but not all kits can hit 2933 or 3200MHz. I'm reading about Samsung B-die kits, dual rank, CL14 or CL15 etc. G.Skill Trident Z and Ripjaws V seem the best bet but they are quite expensive. Should I go for these or just be happy with a 2400MHz kit?
SSD: (SATA) If I go for the 1TB, the Crucial MX300 is considerably cheaper than the Samsung 850 Evo which is the standard suggestion, any other alternatives?
HDD: WD Black 2TB, classic and safe choice
Monitor: Getting a Dell for the warranty, buying this locally. . Thinking about splurging for the Dell U2417H which is 24inch 1080p, or a 25inch 1440p U2515H/U2518D? definitely want the height adjustment
Keyboard/Mouse/Speakers: probably from Logitech for the warranty, suggestions? buying these locally. Z623 for 200W RMS?
OS: Windows 7 or 10, I still can't decide, I read all the time about Windows 10 screwing something with every forced update.

And where to buy from? Mindfactory.de, amazon.de what other places have good prices?

Well I've got a Ryzen R7 1700x.
The stock cooler works really well and quiet and looks good.

Go for a M2 SSD, my machine boots from cold to desktop in about 5 -7 seconds

You mean R7 1700, right? Yes, I know the stock cooler works well but I may not overclock at all in the beginning, that's why I want the higher clocks out of the box.

You mean M2 nvme or M2 sata? nvme ssd is faster but much more expensive than sata ssd and the difference between let's say 960 evo and 850 evo won't be very noticeable for my tasks. And I'm going for 2.5" SATA by the way.

nvme, mainly for OS and select games.

and yes, my mistake its a stock 1700.

I don't know how much more the 1700x is over the 1700.

I've got a GTX1070 in my rig, but I got mine before the cryptocurrency guys killed the market.

Case: Get another fan and mount it in front. I recommend be quiet!.
PSU: It's very good, always stick with Seasonic or Super Flower.

CPU: If you're most interested in gaming, then take the R5 1600X. It usually performs better in games than R7 1700X, due to higher clock speeds and the fact that most games use less than 4 threads.

Cooler: I recommend Scythe Kabuto 3 (read the review) or something from be quiet!. Noctua are too expensive for the same performance.

Motherboard: Go for something with B350 if you don't plan to do extreme overclocking. ASRock Fatal1ty AB350 Gaming K4, MSI B350 Gaming Pro Carbon and Asus Rog Strix B350-F Gaming look good to me. Gigabyte GA-AB350M Gaming 3 lacks the radiator on the SOC (upper) MOSFETs and that's not good.

GPU: If you get a FreeSync monitor, then RX 580 8GB is the obvious choice. But depending on how much the rest of your components will cost, maybe try for a GTX 1070. Check this youtube video too and you'll find other games tested on these cards, on the same channel.

RAM: After you choose the motherboard, look on its site for the Memory Support list and you'll find there all the memory modules tested on that MB. Go for at least 2666 Mhz, but 2933 Mhz and CL15 should be your minimum choice, IMO. And don't forget to update the BIOS. Example here.

Monitor: Try and get a FreeSync monitor, there are some nice 75Hz from LG. IMO, IPS is a must and look for it to have VESA mount too, and then you can get a monitor stand (somenthing like these) and adjust it however you want.

Speakers: I would go with some Edifier bookshelves like these. I would avoid Logitech for speakers, but for other pheripherials they are rock solid.
Here's a great youtube channel where you can listen to different comparisons between speakers (listen with headphones), then decide for yourself.

If you want a mechanical keyboard, I think Logitech G413 is an excellent choice. Regarding the mouse, I find the SteelSeries Rival 500 to be ideal for me (I don't have it yet, but hopefully I'll get it this Christmas).

I would also recommend you to buy some good thermal paste, like Cooler Master MasterGel Maker Nano or Noctua NT-H1.

Ok, thanks for all the tips and links, will look into them:)

Any decent cooler should be fine with Ryzen. The 1600/1700 stock cooler is slightly behind a 212Evo and a bit behind a Cryorig H7, and when overclocking it's usually a voltage wall that is hit rather than a temperature one so top notch cooling nets very little speed improvement. I'd second not going Noctua or any other premium solution, unless you plan on upgrading some time in the future and don't want to double dip the spending.

For motherboards be aware that MSI still has some problems with getting full RAM speeds, otherwise any decent B350 board is fine. However, if you think you may upgrade the processor to Ryzen+/2 at a later date then an X370 board could be a good choice if you don't want to do a motherboard upgrade at the same time. There aren't really any bad AM4 motherboards except one that has been discontinued.

For 1080p 60Hz either a 580 or 1060 is fine. I would have thought for 2000 Euro both the monitor and GPU could be improved upon over those if you wanted. Ryzen works a bit better with the AMD card than nVidia but the comparison is pretty even if you don't want adaptive sync or higher refresh/ res. My 580 handles TWitcher 3 1920x1200 60Hz absolutely fine, but a 1060 does have a small advantage in TW3 benchmarks.

As per poster above, check vendor QVL lists for RAM compatibility once you've picked a motherboard. The inter CPU cluster communication on Ryzen scales with RAM speed so it is more important to have fast RAM than with most Intel chips, but that does have diminishing returns. Samsung B die RAM is best, but it carries a hefty premium in cost. Personally I went with standard Corsair LPX 3200/CL16 which works fine at nominal speed and timings, since the premium for 3200 over 2400Mhz was small but the difference for CL14 (b-die) vs CL16 was huge.

For SSDs the choice is really whether you want NVMe or SATA (M2 or standard). You generally would not see significant speed differences between NVMe and SATA to justify the price difference.

If you happen to have a retail (not an OEM) Windows 7 (or 8 I presume) license already you can use its key to get Windows 10 for free. Sounds slightly dodgy but it's all done through MS so they are fine with it.

I have a G610 and G403 combo for KB/ mouse and they're pretty good, especially the mouse.

For comparison I bought a new Ryzen system a few months ago- R7 1700, 16GB Corsair LPX RAM 3200/CL16, Asus 580 (literally the only 580 in stock at the time), Corsair 550D case, Gigabyte Gaming 5 X370 MB, Crucial 525GB M2SATA HDD, EVGA G2 550W PSU, G610/ G403 KB/ mouse for about 1200-1300 Euro equivalent. It has basically worked perfectly since and handles TWitcher 3 no hairworks at 60 fps on 1920x1200.

Wife and i bought for Black Friday Dell UltraSharp U2414H for 207€. Couldn't find anything better for that price.

Btw AMD doesn't officially support Ryzen CPUs on Win 7.

the Ram is an issue because people are used to Intel chips where big numbers = bettter... a Ryzen cpu takes Ram upto (but NOT over) a certain speed so its far to common to pay for faster rams only to find the CPU doesn't read it--- or only reads one side!
when you know what cpu you want goto AMD and look at their tested-works list for RAM and get something on that list... even you pay a bit extra its well worth it

Windows 7 has 2 years to go before it gets tossed in the bin for good... Windows 10 (with auto updates disabled) is the only real option you have

p.s, not a fan of the Gigabyte boards... they make good stuff but their Ryzen boards have driver issues they have not fully sorted yet