Hi Sascha
When I returned to the hobby I was amazed by the quality of some kits and at all the AM stuff that you can add. You can get a pretty loaded up kit for $45 and then spend double that in AM stuff

So what I do is I try to stick to the newer better quality kits, read reviews before I buy

Then build them OOB.
I have used some AM stuff but I never bought any of it, it was always included with the 2nd hand kits that I bought off this site
With that said here in the states I use Scalehobbyist.com
http://www.scalehobbyist.com/?gclid=CI6IkvWasZQCFQNfFQodkHdttAIf you click on their Manufactures link it will show you the emblem of the brand and what they make then you can search to see what scalehobbyist carries