The main reason that I like the larger units it that a 4-plex ranges from roughly 1-1.5 million in my market. 

What is the main hang-up with financing, when it comes to adding bedrooms?

I have not seen any "main stream" versions of this just back country engineering but it's a solid concept and works well. 

It is possible the largest investment shift in the last 395 years is some kind of tulip scam and there are elements to compare to that, however we are not talking toys or flowers in this case.

Our lot size is 7300 sq ft and main house is 1700+ sq ft.Location: San Jose, CA- We were thinking to potentially design the ADU such that we could have a wall (or a door) that allows us to separate the ADU into a 1 bed/1bath for self use (or rental) and another part which could be rented separately on AirBnB as needed.

This investment was mainly for the new washer and dryer units in every property.

After I learnt what I had to by making mistakes, hosting open houses, and closing a few deals - I switched to another brokerage that dealt mainly with offmarket properties and investors (both residential and commercial). 

I'm based in the Seattle area, but my main real estate focus is in midwest market (Memphis and Detroit) To be clear, I wasn't making as much as you but I was able to put myself in position to leave my W2 . . . for now.

Currently, we have a 200-amp service to the building, split into two 100-amp main panels for each unit.

Both of these challenges can often be minimized with the right team and guidance from an experienced investor.As @Jay Hinrichs mentioned, appreciation is the main driver of wealth in real estate.