If there is a similar duplex you want to build in your area you can try to connect with the listing agent to see who the builder and architect is to learn more about the process.

A couple summers ago, I worked as a construction laborer for an architect who was originally from Canada. 

Thus far, I have secured financing, have a general contractor lined up, architect, real estate agent, and recommendation for a couple of good builders.  

You will need to find an architect and builder to determine what you want to build is up to the zoning code.

He’s going to be sharing a 60 min, no-BS class on everything you need to know about designing, permitting, and building an ADU — such as costs/timeline, how to get approved fast, how to negotiate with architects/GCs, utility connections, etc.I was wondering, what’s one question you have about ADUs?

First time land developer, when a town asks for a certified plan, does this mean you actually purchase a plan from an architect or the plan websites first?

Very expensive and requires an architect to move the lintels.In place rents are at $0.86 PSF and market should be $1.00 PSf, provided the clear height doesn't deter too many tenants. 

Yet another plus would be my girlfriend (who I may or may not be able to convince to join me in such an endeaver) works as an architect both professionally and in a side business of other young architects that specializes in residential remodels and ADU conversions.

It’s a good idea to walk through with an Architect and contractor to get an idea of the potential issues, cost and timelines.

To complete a lot split you need: original parcel map, seller permission and cooperation, engineer/architect new plat plan, ask for a permit from county or city planning, pay the fees, the planning department may ask for a hearing, the neighbors can dispute if there is not enough parking or use is not similar or contiguous, this takes time, maybe they say yes, split is recorded, after that's done you can close.