Consider more than just rental income, such as, prior tenant history, civil and criminal background, employment history, number of occupants for the size of the home, desired move-in/move-out date, etc.

They first said they were waiting on court papers, then the following week they said a court date.

Learn where to look for the date of manufacture and make the seller send you a photo.

I’ve only been in real estate 4 years, not 40.Old school out dated favors the big guys.

Vedran Sehovic Hi Vedran,  I did some more research and see that VBRO and AirBnB have a lot of inventory / unscheduled dates.  

Quote from @Robert Ellis: new builds set the price premium in every zip code I've ever studied. in addition new builds don't take 9 months. we just built a house in 60 days. we wait till permits are approved and shovel ready, investors buy land cash, entitle, contracts, negotiate with financing, place financing when we are ready and break ground. but we build the same over and over and don't go outside our Floorplans 60 days from Dig date maybe.

My out of date layman's opinion is that if the building ever had six or more units what you'd wind up with is one deregulated apartment and four regulated units. 

You would then finance the property at a later date. 

I usually just send a screenshot of a bank accounts, but I have seen others get their bank to write an official dated letter saying they have at least X available to withdraw immediately.I would not consider the letter you attached as a proof of funds, nor a contract offer, its more like a letter of intent? 

Unlike personal property, real estate also requires agreement on closing date, repairs, etc., so even if list price, cash is offered, another term might not work, so likely no way to hold a seller to sell until they actually sign an offer.