Even the high-priced gurus give you a basic introduction for free, or low cost.Look into Brad Sumrok.

The bathrooms would be directly above each other) We have drawn up a basic floorplan ourselves but we would still have to hire an architect etc.

This is a basic check.  

ADUs can come in different forms, such as a detached cottage, a converted garage, a basement apartment, or an addition to the main house.Before purchasing a property with an ADU or historically reserved property, you should consult with a local real estate agent or attorney familiar with the local regulations.

Basically there is a base fee + monthly and you only get back 50% of the unused portion.   

Any one know where I can get a basic rental agreement form?

In fact, I am considering the same idea: Renting my current town house and looking to get a single family home around germantown (and possible other areas) in the 300-500k range and house hack it.Say you get 3 rooms and a basement.

I have a basic app half-built in PHP on Symfony using the Zillow API, but again  - the 501 error comes up a lot.

On the other hand, if this is a basic rental, I can see the value in simply telling the contractor, "use builder grade products" and allowing the contractor to choose the material within a price range you set. 

A basic floors walls renno is getting quoted timeline of Thanksgiving on our block...one crew doing  10 homes.The shortage is not housing its manpower