You will have no more purchasing power without a Realtor, and walking in without representation could cause you to be "oversold". You will be walking into Model Homes that have all the glitz and glamour, up all of that comes at an upgraded price. You will know what the additional costs are, but will you really be able to control yourself from going overboard and feeling you must have it all. Having someone to represent you will allow for a buffer and give you someone whom you can discuss the cost-benefit analysis with. It also gives you a an extra set of ears to hear what your eyes are not listening to.
Some advice I give clients when they are buying a new home: 1) Don't purchase the Model. Most people are visual, they can get a sense of living in a space based on seeing it. Therefore, in most new home communities, the Model home is the one duplicated. When it comes time to resell, having something different than the norm is a benefit. 2) Check for the little things. You are seeing things completely decked out and furnished, but are you noticing how many hose bibbs there are and where they are located. Do you have an exterior electrical recepticle and will it be enough to run your Christmas lights. Is the exterior lighting sufficient for your future needs (ie: flood lights on the corners of the home). Addressing these little issues upfront will save a lot of additional rehabilitation costs if you were to have them installed later. 3) Get clarificaation on the finishes. Knockdown ceilings vs. Smooth Finish, 5 1/4" baseboard vs. 3 1/4" baseboards, Shoe moulding over hard surface flooring, Door hardware finish (and making sure it matches the hinges).
Long and short, the Builder will probably hand you a specifications sheet as an aswer to your questions. But the amount of detail you cover up front will definitely make your end product that much more enjoyable for you.
Best of Luck, and if you would like to have a referral for the area you are considering buying in, please feel free to contact me.