However, we cannot live off of our retirement accounts today and we really need to diversify our income.For that reason, we plan to take on a mortgage when we move and to use the proceeds from the sale of our home for real estate investing. 

I'm assuming the reason rents are so low is because the current owner lives in the 4plex, my guess is the property may be owned free and clear, resulting in the owner not caring about the low rents. 

If a seller wants cash in less than a month, wholesaling for 40k will get the job done.Whatever the reasons, did doesn't matter from an investors perspective.  

If you go out of state, there is no reason to constrain on Dallas until you have done your research.I would expect that some who use neighbourhoodscout do it because it saves them time and money, not because the service is altruistic. 

It has tenants, I have had one month of vacancy since 2012, I would prefer to sell it without an agent, however I worry that there will be dozens of investors wanting to walk through the place, disturbing my tenants, making them antsy and the investors then low ball or otherwise do not generate reasonable offers.What is the best strategy for making sure the potential buyers are serious before letting them in? 

Don't give them any reason to deny your claim.

For my own reasons I want to now get out of this investment.

One of the main reasons for me to 1031 exchange to a bigger building is that it is almost impossible to take all the equity out when my father's income has not been good enough the last few years.

I have and idea of what a reasonable nightly room rate could be charge per based on what else is available in the area and my present experience in the hotel business here. 

And the reason is if you contribute funds into tax-deferred account you will not be able to use those funds until you retire.It is possible to use a self-directed IRA to buy investment property, however you personally can not benefit from this investment until retirement and you would not be able to use FHA loan.