I really don't get it, why is the word "guten" used and not "gute". This isn't even the accusative case.
I think because "keine" makes the adjective to decline in weak declinsion (like in the case of definite articles)
Almost! Mixed inflection = indefinite articles or possessive pronouns. http://en.wikipedia.org/wiki/German_declension#Mixed_inflection.5B6.5D