Most existing inventory being sold now is selling at a 10x revenue multiple though using 2021 rental income, which is up from pre Covid. 2 years from now you could easily be underwater just breaking even on your expenses, if your lucky.  

I would probably do it unless I was keeping/maintaining the existing radiator or HVAC system.

I have not seen that in a retainer agreement, but it doesn't mean it doesn't exist.

When buying an existing self storage facility, some operators separate out the value of the business and retail from the actual facility to lower their property taxes.

Also are you tying in to existing Storm Drain and sanitary sewer or are you putting in septic tanks and leach fields? 

I will let you know most of my clients are able to use low money down conventional loans in your circumstance but a major requirement will be how much equity you have in your existing duplex. 

I am very familiar with the process for acquiring and analyzing an existing structure but have no experience building something from the ground up. 

When a tenant refuses to respond to any means of communication, that indicates they're trying to hide something and I'm right almost every time.What red flags do you watch for with existing renters?

Contact information for existing/previous property management company.Purchase Agreement Clauses for Buying Tenant-Occupied RentalIf you’re considering buying a tenant occupied rental property, there are some documents you want to acquire for review prior to the closing.

So you still need that day job to keep buying, or to actually refinance your existing properties.