No you dont need to be a scientist to get a NE under §19. See paragraph (2) 3
http://www.gesetze-im-internet.de/aufenthg_2004/__19.html
1) Is Contract sufficient?
--> depends on the case worker. Some might want to see university degrees or a letter from your employer which says how great you are

2) what special should be in the accompanied letter?
--> you have high university degrees, excellent experience, you are a specialist blah blah blah
3) In case of failure: what are consequences (e.g. for next applications for PR)?
--> i see none if there is no major rejection reason
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The salary level is approx. 66K now after it has been reduced from 84K since several years now. A law has been passed by the Bundestag to reduce this to 48K. Final approval from Bundesrat is still to come but will probably be passed in the next 2-3 months.