First to answer your questions:
Originally Posted by
Caribgrl
Is there anything I should know in advance before booking this? Is it even too soon to book now?
Never too early to book, unless you need the points for something else before you go.
Originally Posted by
Caribgrl
And are these bookings able to be cancelled w/no penalty?
Typically free cancellations, but read the terms before relying on blind advice here.
Originally Posted by
Caribgrl
Or can I just put it on hold?
Nope
As others have said, be cautious of the very pitiful value of the rewards. What's the value of the points you're using for the car ($$ it would cost otherwise vs. how many points it will take)? And what value can you get out of the points otherwise (from a hotel booking, hopefully, as that's usually the most value)? However, everyone's situation is different and values things differently, so if you feel the best value for the HHonors points is to book a car, don't be persuaded by the opinions here.