It all depends where you are, use your best judgment- Just don't be pissed off when your bike is laying on the side when someone who has a bug up their a22 doesn't like your parking job.
Carmax is for suckers. You are getting screwed if you pay sticker price- but if you can't/don't know how to negotiate I suppose it is your money. 30 day tags are like 30 bucks or so and you will register the car at the Bmv in Ohio.