I can't hardly stomach the markup involved in letting someone else manage everything.

JAX is a great place to get involved in REI!  

Jeff I message you so keep an eye out for that, I would love any info I think different level of involvement would be more interesting.

How much time before my sale closing date should I get the qualified intermediary involved? 

When you have the right kind of knowledge the options available to you become clearer, you understand the parts involved to fix any situation.

Are there any other costs involved when the buyer pays off the loan?

@Chris Clothier  my points are directed at ANY mid west deep south rust belt major city and sub 50k rentals  it goes to the very long debates we have on BP about the risks involved with these homes... in some markets just a touch higher will pop you into something safer but in general.. as you state its not reality that ANY rental in almost any part of the country will perform to the degree that one can count on consistent reliable non interrupted income stream... that's my point.. so when you have folks think they can buy 10 like the OP said and get 4k a month like its a bank CD they need to understand you you and others point out it just does not work that way.

Also depending on the type of loan Standard vs Steamline, will have an impact on the # of different folks involved and who you can use to get the work done.

In my opinion I have found a tremendous benefit to working with someone else (as long as they are involved and being productive)1) having a partner gives you someone to bounce ideas off2) To me it's more motivating (ex, let's see who gets in front of more people this week)3) They can help finance your growth  with you.As long as you and your partner are motivated and skilled enough to succeed, you will do more than twice the amount of business that you would do alone, and make half of that.Hope this answers your question.

For the past 8 years I have been involved in college athletics.