Be careful with stock plans. Houses are designed differently if they are intended to be built in Quebec or in Florida. Different contractors I work with have grumbled about internet plans and how they dont have room for insulation or the vapor barrier details are all wrong for the climate zone we live in.
Should you do stick or modular? What is your intent for this house? Is this a high end spec/custom? or a working class/entry level housing?
Are you looking at being the GC and hiring crews and pocketing the largest piece of profit? or are you going to hire someone to run the project and end up with half the profit with a lot less of the headaches?
If you have an existing site, you have a bunch of the development headaches out of the way (water, sewer tie in, ect) If you want to reuse the foundation, it will probably need an engineering evaluation.
If you go the self GC route, your next step is to buy plans or have them drawn, and then put those plans out for bids.
If you are planning on using a GC, find one you like, and ask them if they have some in-house stock plans that they have built before. If a contractor has built a plan before, they will usually offer better pricing because they know the plan and there are less unknowns that might potentially pop up. (and they don't have to spend time doing quote/takeoffs because they can just pull the file from last time and update the pricing)