Right now - we run most of the income/expenses for all properties out of one "managing" checking account, and then just designate every expense for the property it's for, thus allowing us to do the bookkeeping from there. 

Turning that residence into a rental property will void that designation and allowing it to remain is fraud.

If you like - please better describe your 'professional' designation.  

The house would be designed in "panels" that would be prewired and have junction boxes where the panels connected.

I own a small design/build furniture company located in Seattle, and I have been thinking about using my furniture, and my design sense, to start staging homes.  

Used to be fish in a barrel; now it's needle in a haystack?

These will be less expensive options but be aware that the municipality might be asking for more.If the municipality is asking for zoning issues, ADA requirements, historical items or design changes, etc. then get an Architect.

This was never designed to be a rental property, but it ended up one so now we are trying to make the best of it!

I am currently working on my marketing plan and designing my postcard campaign. 

I have seen this in a couple units I have rented in Seattle.Does anyone know a good structural engineer/architect in Seattle who can design an affordable attic and basement remodel for an older home?