Ok I'm really confused. Your accident discription is not clear at all.. This is coming from a claims perspective.
If police attend the scene of an accident 95% change someone will get charged for neg driving.
Your witness is not stand alone, you can't use them. You need a independant witness like someone in another vehicle or a pedestrian.
Your 2nd offence is pretty clear, If you have to display P-plates then do it, there's a good reason why they make you do it.. There's no point risking that crap these days when you guys have only 4 points.
You're aguement against this suspension quite possibly won't stand up in court. You obviously don't drive for a living and you've had more than one offence in the last 6 months.