I now have three tenants and I lease part of one of the properties back to my business as a storage yard (so 4 streams of income).

@Jordan RegierA garage is definitely a benefit for storage, recreation area, etc.  

yeah you are likely looking at art studio/content creation type spaces or maybe some startup that needs a bit of storage or warehousing while they get going. 

I put in a well, brought in electricity, a gravel driveway, a septic tank, and a fence around part of it for my horse.  

I have been looking into carwash, storage units, multifamily rentals, and other ideas.

The property features two 1,400 sq ft suites on the main level (one currently leased) and over 3,000 sq ft on the upper level, with 750 sq ft already occupied, 3 small office spaces (+/- 250 sq ft each), and a basement tenant with 1,400 sq ft of storage space.The building generates $6,000 in monthly gross income from its five tenants, but with full occupancy and market-rate rents, it has the potential to bring in $10,000+ per month.Given its historical significance, stunning architectural details, and location, I’m curious about your opinion: Would this property be more marketable for sale with or without the current tenants?

The early 2000's credits increased prices, but they were tanking and the stabilization was a good thing. 

IMHO Have campaigns for phone text email follow upHave a phone system Have a text system Have an email system Have chat both external and internal Have webforms Have RVMHave conference roomsHave file storage Have a CRM attached and seamlessly churning data  I use calltext.com however I also own it. 

In my case, I have residential rentals in one LLC, commercial properties in another, self storage in a third, and my real estate company operates in a fourth.

Would you replace a current functioning 1000 gal septic tank to a 1250 gal tank in order to list my flip as a 4 bedroom as opposed to a 3 bedroom.