1. - If you are not a skilled bike-mechanic and have a full compliment of tools and a working knowledge of how these things work - and you have built a bike up from just a frame before - add at least $200 to the price of their bikes. The $200 is around what a shop would charge to build it for you.
2. - You will not have a warranty behind the bike. So after it's built, expect to pay for a tune-up from a bike-shop shortly after you get the bike built for you. Things like cable-stretch and derailleurs needing adjusting are normal. If you bought your bike from a bike-store, this service would be free. Buying your bike off the internet means you are on your own.
It's your money to spend as you wish. I hope you have lot's of it.