Most importantly, don't ride any bike or use any component that you haven't thoroughly test-ridden before the event. And that doesn't mean once round the block, it means a 50-mile ride minimum.
New bike? Don't think you will be disgraced if you turn up with anything less than top of the range. A good sportive bike is something that you should be comfortable with all day long, yet which has that race feel. Pay attention to your contact points: saddle, shoes, bar tape/short finger gloves (didn't they use to call them track mitts?)
Tyres: You are strongly advised to use tyres with an anti-puncture layer (best with a bit of sidewall protection too), a casing with a high tpi figure, and a minimum width of 23mm. Inflate to recommended pressure with track pump. Carry at least two spare inners.
Cycle computer: it's probably best to set it to miles rather than km for this event. Only distances in miles are given on the route card.
Gearing: Compact or Triple chainrings are not essential, though use them if you've got them. A 42-tooth inner ring should be adequate for the steepest hills.