Welcome @Niklas!
it’s pretty hard to do anything wrong here 
We have many german residents that could also help you out 
@xsynatic @Mainflow @Creavenger @Benjo are a few of them 
Also since you are new, we made a few threads that could really help you with building an esk8, especially since it all seems a bit complicated at the beginning with different Vesc and battery cells, battery chemistry, boards etc…
So if you don’t mind, have a look at some of these 
Glossary of Terms
Battery Basics for Beginners [Serious-ish]
[WIKI] Trusted Battery Builders (Serious)
Builder’s Wiki-start here! (SERIOUS)
Thats a lot of reading already haha.
I also want to note that 500 is very low and to build something good at that price is really hard when ‘‘China Boards’’ like Exway (pun intended) make amazing boards for the price.
May i ask how much range you want and what wheels you would like?