I also use the Costco/Citibank VISA cash back card to pay for expenses.  

Our current mortgage terms include a late fee after 5 days, so they’re already paying extra each month and have to split the total monthly payment up between 2-3 payments when they get their pay check.

If the new owner pays on the loan its not "equity skimming" from what I understand of it.

I created an electronic google doc time tracker: Time LogContemporaneous time log of rental real estate activitiesActivity DescriptionTenant recruitmentTenant screeningNegotiating and executing leasesOverseeing repairs and maintenanceCommunications with tenants and vendorsTravel timeResearch for potential rental real estate (pub 925)Acquiring rental real estate (pub 925)Paperwork/bookkeeping/bankingResearch and purchase of materialsRent collectionEvictionOn-site cleaningBill paymentOther:Time SpentDateMM/DD/YYYYSubmit

Today's Americans want to live on Sunset Strip and pay Main Street USA prices.

There's not going to be a nurse who will pay $4000 themselves to rent a 5/2 and the property wouldn't cash flow if I rent to 1 nurse for lets say $1400 / month. 

Is it a small enough amount of money and do you trust them enough that you could pay a month in advance by mail?

yes create the addendum but realize the tenant who has been paying could ask to be reimbursed for these costs as well as not accept the addendum.

We typically pay somewhere in the range of $3500 for a new, basic furnance, including install, if there are no other modifications to the system required.  

Grow wide first, then deep (pay off)- your little expenses add up fast