Audition = Music composing and production?

No, I'm afraid you can't. Audition doesn't handle MIDI at all (this has been discussed ad nauseum in the past - we're not dragging all that up again). Audition's VST compatibility is that it works fine with VST effects, but doesn't handle VSTi's at all. Basically, in the terms you are describing, Audition isn't a DAW as such - it's an audio editor. Yes you can use Audition to mix music, but what it isn't is a music creation program. This is unlikely to change, either - it would require the major seat holders to need it before that would happen. So even though there is some goodwill towards the idea within the development team, it's not up to them; this is a corporate decision that none of us can alter in the slightest, it would seem - and it's been like this for a while.