We need to be almost mechanical about it. 

There are all kinds of engineers, such a structural, mechanical (HVAC system) and electrical (for wiring, etc.). 

If I was to guess on cost based on the pics I would throw ~$15k for carpet, stud walls with insulation, new ceiling, painting, electrical and mechanical. 

When you get into triplexes and fourplexes those are considered "multiple family occupancy" and while they fall under single family funding mechanisms have different down payment guidelines.

If you're going to even possibly have to change out any of the mechanicals (hvac, water heater, etc.) or deal with major plumbing or electrical I would go to those right away, too.

You may want to look into joining a syndication deal or buy a duplex just to see the mechanics of REI then scale up.

If not, there’s just no mechanism for enforcement right now with the moratorium on evictions, but it doesn’t hurt to post it.Here’s an article that even has a Florida attorney confirming you can still send out notices: https://www.clickorlando.com/news/local/2020/04/10/despite-notice-florida-tenants-cant-be-evicted-during-governors-moratorium-on-evictions/?

Some of the plans I reviewed do have an efficient design to accommodate the mechanicals esp if you decide to go with a crawl space in lieu of an expensive full basement. 

Don't know about KC, but most jurisdictions allow only licensed contractors to pull electrical, plumbing and mechanical permits.  

Consider your tenant's complaint as a good alarm mechanism that your house could sustain structural or fire damage that a little bag from Home Depot or Lowe's could have prevented.