The broker can chose to terminate the contract or the seller can but even in this case many will still require payment if the home is sold during the timeframe the listing agreement outlines. 

To get a better price when sold 

Funny I sold a duplex in Chicago for this exact same reason.

One item to consider is the elevator, the cost of which surprised me.  

Another item to consider in your plan is often times the utilities are not going to be separate, which may not be an issue when you live there but if you end up renting out your dwelling when you PCS elsewhere, your new tenant is not going to pay for their utilities plus the accessory dwelling unit.

Even if you hired a designer as well you’d still save money versus paying the $50,000 .Searching listings online for homes that have sold as flips and see what kind of design they use or go to open houses of flipped homes .

I know that the fact it hasn't sold is concerning, but what should I do? 

I have purchased and sold homes with a realtor before but have a new one I'm using as my old one moved away.I found a home I want to buy so I asked my realtor if she could get any information about the current renter Payment history and the existing lease.My realtor came back and said the sellers agent was very short with her and "yelled" at her through email.

An interesting situation came up where one potential buyer proposed an Equity swap to be used as a down payment, where I would take ownership of their property in Waukesha, and then I would seller finance to the buyer the remainder of the balance owed on my sold properties. 

We sold them both, seller financed, in the 1995-2000 time frame for $77,000 and $83,000.