[wrxtasy]

I'm new to the whole "Streaming-box game". I've been using Kodi on my laptop for over two years now but I want to get an device with the sole purpose of playing media files. I use both locally stored files (mostly MKVs in 720p or 1080p) and files I have to stream (Amazon Prime, Netflix, Hulu, HBO Now). The locally stored files would either be accessed via a NAS or via my external harddrives. I might add LiveTV later on, but that's not something to bother now.

I've been Beta testing this device since mid August and it keeps getting better with each Firmware update due to the WeTek developer - Christian Troy knowing his Android stuff inside out. And no I have not been drinking too much from the WeTek Koolaid fountain.
With this box, you really get the best of both worlds. A full blown Android Lollipop 5.1.1 system without the Android TV OS limitations already mentioned, and you also get a Widevine Level 1 certified device to playback full 1080p HD video streaming from DRM protected Apps like Netflix, HBO Now etc...
No other Android boxes running the regular Android Lollipop 5.1.1 offer this in the one package.

Now based on the posts in this thread I think this box would be ideal for me. Android ensures compatibiliy with the streaming services I want to use and being able to run Kodi would be the cherry on top. Other than movies and TV series I'd watch NBA games, but I don't think that should be a problem, right?

If NBA is one of those paid for Streaming DRM services, then you should not have an issue due to the correct Widevine certification already mentioned. Also please read up on page #1 about known Kodi playback limitations regarding mpeg2 .vob files with any AMLogic platform including the Core.

With this in mind, I don't really need to bother myself with 10bit, 8bit, 3D, HD Audio and all that stuff, right? It might well be 4-5 years until I'm gonna buy a 4K TV and until then the WeTek Core should be great for my purposes, right?

I'm have virtually the same requirements as you. I will wait until my old 1080p TV fails before I upgrade to a 10bit capable 4K model. I may even consider some HD Audio Equipment then as well.
In the meantime the Core has now become my all in one go to media player. In my opinion, WeTek have got the balance right for users with requirements like yours and mine.