An architect is your starting point - One that specialises in custom residential work, and has some years of experience.
Not a large firm that designs industrial/commercial buildings primarily, or one with less than passionate figure-heads leaving the work to the a few green youth behind a pc. Get someone who designs on physical paper, those sketches are art :)
It's important to note that good architects do come at a cost, but they come with value too. The value of starting at the right point and working in the right direction outweighs the apparent saving of a tract builder or stock plan.
Also note that two houses costing the same $ can 'live' very differently, and this is where the right professionals are important.
The rationale behind an architect in a nutshell, is this: You need a design that works for your lifestyle & needs (current & future), as well as your land, your climate and code requirements, etc and is architecturally sound.
Stock plans will give you none of that, and will give you numerous ssues (angled walls, poor lighting, expansive closets because the Jones' have them, prominent garages, etc are some of the common ones) Architects are trained to do this and more.
Once you've found a good architect, ask them for recommendations for contractors. Kitchen designers too!
Get reviews. On everyone, for everything, always.
And be prepared to have huge setbacks, but try to enjoy it all!
Q