Welcome to the world of speed and smooth riding
First of all make sure you have a comfortable pair of cycling specific shorts and a comfortable road specific saddle as you'll likely spend more time in the saddle.
You'll still have to avoid objects in the road I'm afraid but your carbon frame should help dampen any vibration from the road
Whereas my mountain bikers use predominantly the rear brakes on the road if you simply hold the rear brake down your back wheel will lock and cause you to skid so get used to gradually braking with the front brake- you won't simply stop and fly face first over the handlebars which people expect.
Helmets are a debatable question but in general you'll be safer in case of some types of accident if you wear one.
The best advice I can give however is simply get out and ride. Have fun and learn from the many mistakes you'll make just let you did when you started mtb'ing
@bruzzbruzz- road and mountain bike crank lengths differ rarely so the likelihood of difference is minimal however the advice on lowering the pedal at opposites to the corner does lower centre of gravity and gives additional grip into a corner.