I recently left working as the Director of Sales for a national homebuilder where I led my team to over $120,000,000 sales in 2012. Thus, I know the ins and outs of working with builders and am truly an expert.
The answer to your first question has been handled very well by the agents below. Most builders welcome brokers and agents but require that the agent accompany the customer on the 1st visit. Give me a call and I will be glad to discuss this further with you.
With regards to your second question, it really is a function of supply and demand. Conventional wisdom holds that a detached home will appreciate faster than an attached home. However, I find that conventional wisdom isn't always so wise and could show you numerous examples in communities similar to Clarksburg where the appreciation was similar.
I would recommend that you focus on the home that best suits you, is within your budget, but most of all has the features and spaces to make your every day living spectacular.
Feel free to call me any time. Helping buyers is what I do.