You should honestly take the time for proper drawings to be completed. Even if you like the look of the house you have shown, there is no point spending such a large amount of money on a project that does not suit your needs, or fit properly into your site - and was designed for someone else.
Considering the amount of money you are about to invest you should talk to an architect you like (they don't have to be local!), and they will gladly take the time to answer a lot of your questions for free - its a buyers market, they need work. A good architect can address any planners concerns through pre-planning meetings, and make sure you get a home that suits your needs. Your site sounds wonderful and should have a home that compliments it.
It sounds like you have a potential good project, don't ruin it by rushing, engaging a builder without drawings or compromising on what you want - you will regret it.