Hi there... I don't know much about the Giant line... I tried them but they didn't fit me so I kept going...
Have you test ridden several brands? Lots of great bikes out there... the key is getting a frame that fits well... if it's the Giant for you, then cool! You may want to check out Road Bike Review to see what others think of this bike and also the price of it... pretty comprehensive reviews...
as to gear... shorts definitely. You can add shoes and pedals as you can afford it, but I personally think you can't afford NOT to buy shorts. They prevent chafing and help prevent saddle sores... since they are made with no big seams that rub in all the wrong places! Be sure to never, ever wear shorts more than once without washing and after a ride, change as soon as ya can to prevent yeast infection since they will most likely be damp after a hard workout.
good luck and hopefully someone who know Giant will come and help ya out more!
There is a fine line between "hobby" and "mental illness".