FYI - it sounds like you need to do a good bit more research before you purchase an AR. That said - you are posting here, so that's a good start on your part.
You've posted a good many separate questions, so let's break them down:
Would you pay 2 grand for a custom DD rifle? Too much, could I do better for cheaper??
DD makes top-notch rifles. If that rifle with those specific features are what you want and need, only you can determine the value. I will also say that BCM makes rifles of equal quality, and they typically run a few bucks less. I suggest you check them out as well.
I cant build an AR I dont have the knowledge or tools so please dont tell me to build my own. Even though thats kinda what I did at DDs website.
You can build an AR. There is plenty of guidance available, including many Youtube videos showing you exactly what to do. As Robert said, only basic hand tools are needed to build a lower (punches, hammer, needlenose pliers, and a vice would be healpful). Alternatively, you can buy a lower already built.
One you have a lower, you can buy an upper online and have it shipped to your door. Again I recommend BCM. Installing an upper to a lower requires no tools and requires about 15 seconds of your time.
At DD's website, you did not build an AR. You just picked out features.
How can they deliver to your door? Isnt there a background check process???
They can deliver a complete firearm or lower (either stripped or complete) to an FFL. You will have to go to the FFL to fill out the paperwork and pick it up. They can not ship a firearm straight to your doorstep unless you are an FFL.
Uppers are not firearms (they have no serial number), and can be shipped right to you door.
Also anyone familiar with the 300 BLK round? I chose 5.56 but never seen a 300 BLK or hear of it much.
You need to give us more information about what you will be doing with the rifle. I also recommend you do a bit more research on this subject.
5.56x45mm is the traditional AR-15 round, and is suitable for defensive use, target shooting, plinking, competition, hunting (up to whitetail in some area), and general fun. .300 Blackout is a .30 caliber round that really shines in suppressed use. It's also an option for hunting deer-size prey at shorter (<300 yard) ranges. .300 Blackout ammo also costs MUCH more than 5.56x45mm ammo typically, so take that into account.