and / or
A self-employed planner who really knows her oats. The gender choice is deliberate. Women are far more capable at focusing on detail; nitty gritty detail. And thats exactly what you need now. You need someone who can answer this question simply , honestly, quickly, first.
Why? Because your design taste will be changed by the process of planning for building it. Exactly the same way that drinking cheap red wine , with persistence, evolves into the odd glass of serious claret.
Research the planner market. Do that by reading widely. Read the Design Access statements` they have written. Does the statement show a well-argued narrative? Or is it sloppy / slapdash? Waste time with many local estate agents. Encourage indiscretion on their part; and remember those who refused. Network like mad.
Then interview one or two. Trust those who want a small amount of cash up front for a quick, straight opinion. And then employ the one who impresses you most.
But solve the water supply issue first. There is a long cautionary tale about that to be found on @JSHarris blog.