I'm not Japanese, but I can still help you anyway.
The polite way of saying "not important" is "taisetsu ja arimasen", while the casual, short form is "taisetsu ja nai".
The negative forms of "kuru" are "kimasen" (polite) and "konai" (casual). The negative forms of "suru" are "shimasen" (polite) and "shinai" (casual).
Oh, and just so you know, a politer way of saying "aoku nai" is "aoku arimasen".
I hope that answers your questions.
