Hey @LaTara G.,
I am absolutely biased! Get an architect. New development is complicated. Whether you have stock plan (off the internet for a price) or want them designed doesn't really matter, they have to conform to code. You will need civil engineering to deal with the slopes, drainage and grading of the land; a structural engineer to make sure that it can resist lateral (earthquake and wind) loads; and the architect will make sure that it complies to the local residential building code (as well as coordinate all the other engineers). They can also give you a good idea about construction costs (in Seattle we cant built a home for less than $150/s.f. right now).
Here is what I would do- print out a picture of the floor plan you like, look up 3-4 different architecture firms in your area and call them up (make sure you ask if they do residential, many focus on commercial), make an appointment and bring the floor plan, make a list of questions that you have for them (see list below), take dubious notes and have them all give you a proposal. The key here is to find an architect that you connect with, do not focus only on price. The relationship between you and the architect is more important than the fees, because the value that the architect provides (great relationships with permitting office, competent staff, availability to get started, clarity in communication,etc) is much more valuable than drawings lines on paper. Also remember that you are going to require a bit of hand holding because this is your first time (the architects will know this whether you disclose it or not), but stress that if the team (your development team) can make it a great experience then you plan to build more.
Possible questions
Can you help me find the right property? (many architects help clients find and analyze land)
What kinds of preliminary investigation report do you need to begin design: geotechnical report, wetland biologist report, ALTA survey, title report, etc?
What does the design process look like in your office? (we all have the following phases: schematic design, design development, construction documents- you want to know timelines and deliverables)
Do you engage with contractors to provide preliminary construction estimates to you designs? At what phases? (you want the first one after the schematic phase- granted it is super rough, but you will know if you are in the cost per square foot ballpark)
What process do you usually use to find a contractor for a project like this? (architects call this phase procurement or bidding and negotiation)
What is the biggest value that your firm brings to my project?
Do you currently have the capacity to take on a project like this?
Will you put together a proposal that outlines what you provide in each phase, the deliverables, and the cost per phase as well as a total for the project?