However, no mainstream index fund like the VOO or some dividend index, got forclosed on.

@Sean Gammons rising property values & mortgage rates have ended the "easy days" where you could buy anything and rent for cashflow.You're going to have to look harder or go into riskier investments.Prior to the crash of 2008, seasoned investors would look at 100 properties, bid on 10, to hopefully get one deal accepted that met their ROI and CoC requirements.

I was able to rent the home for $2600 but the lender is accepting the appraisers rental value of $2050.

I've had a Craigslist rental ad up for weeks with no issues, no discriminatory verbiage, etc and since I had a "run in" with a local RE agent who was trying to force me to take her applicant (who was on every program in the book; not that there is anything wrong with that) I believe she is behind the flagging since I wouldn't accept the applicant.  

In retrospect, I did not negotiate very well; I accepted their counter which was just below the list price.

The payment has a clause: By accepting this payment, I acknowledge and accept the following terms:I am the property owner (or an authorized agent for the owner) of the above-referenced property and I am authorized to receive payments.

Do I need a *business* checking account to accept rent payments and pay for maintenance/repair costs as they arise?

Due to market condition, I accepted an offer which is $20K below asking and additional $20k credits towards closing.

My profit on this sale is slightly less than the requested discount so I am not willing to accept it.

You can't say no to them if they ask if you accept it, but you can likely find a reason to reject their application.