around 600 dollar build, is it worth using pre used Ebay parts?

Hallohannes

I'd like you to help me out on two ends:

Some important information: My is around 600 but I'd rather go even lower and if you do tell me I get some decent performance at 500 bucks I'd do it, but I want at least a 500gb SSD. I work a lot with my pc so I dont want to choose a great graphics card but a mid CPU even though I also want a pc that is decent enough to run games like GTA V on low to mid settings. I live in Germany (if that matters), so  here is my build: Feel free to switch out EVERYTHING im not sticking to this its a concept.

second, Is it worth buying used PC-Parts or should I go with only new parts (remember I rather have mid performance and save 100 thand spend 100 more for just this slight upgrade)

PowerSpec_MichaelB

Welcome to the forum @Hallohannes. Your component selection looks solid, sadly there isn't too many corners we can cut to save much more, aside from maybe storage and memory capacity, starting with a 500GB SSD and 8GB of DDR4 and upgrading later on once your budget permits.

As for buying used components, there is definitely a strong market for used components however there are some guidelines I'd recommend following when you buy used components. First and foremost, I strongly advise against buying used HDD's/SSD's as well as used power supplies. Storage has a very finite lifespan as mechanical drives are subject to failure over time and SSD's have a finite number of writes. Power supplies are also important as you don't want your PSU to die, and potentially have it take other components with it if its built in protections fail. 

Graphics cards are pretty safe to buy as long as you use some basic tips & tricks during the purchase. Make sure when buying a graphics card that the seller has proof that it works. Request a picture of the card to make sure the condition is still good, and request a picture of the card running a task such as a video game or Furmark with the seller holding a picture of their online name and date. This will help prove that the card can still perform 3D rendering and will help ensure the seller actually has they product they are attempting to sell you. Another piece of advice is to check the second hand warranty policy for the brand you are purchasing. Manufacturers like EVGA offer second-hand warranties for products purchased from the original buyer, so you might be able to get a used 10th generation graphics card like a GTX 1060 for a solid price and still have a bit of warranty left over for the added piece of mind.

With CPU's, you need to be a bit more careful. GPU overclocking is pretty harmless due to the locked voltage controls on most cards, but CPU's can have their lifespan and stability greatly impacted by overclocking. When buying used CPU's, it might be best to invest in a locked higher end processor to make sure the processor hasn't been abused with too much voltage. Also check for keywords like "delidded" for Intel CPU's. While it offers greater thermals, it can be a bit of a hassle to deal with when the IHS falls off, or if the liquid metal dries up over a longer period of time. For AMD processors, you don't have to worry too much as they don't really scale all that well with manual overclocking, so a lot of people avoid doing it entirely. You might also find some great deals on first gen Ryzen CPU's thanks to the recent 3000 series launch. They are also extremely uncommon to delid thanks to their higher quality soldered thermal interface material.

Motherboards is another thing to be mindful of. If buying an Intel motherboard, request a high quality picture of the socket to make sure there are no bent pins. If it is an unlocked board, inspect the VRM power delivery components to make sure there are no burn marks or popped capacitors in view. AMD boards are likely a safer bet for the aforementioned lack of overclocking headroom, but it never hurts to thoroughly inspect the product or ask for more pictures.

I wish you the best of luck with your build. If you have any further questions, let us know!