Another question is, if I'm wanting to send letters to potential sellers I'd like to be persistent but how long should I wait between each time I send a new one?

One seller was quite old and sold a commercial apt building so we had a 5-yr balloon and I got a commercial bank loan to cash him out.  

Now its your job to remain in contact, meaning keep sending postcards or letters to your list.

I am not sure the buyers will want to switch it up, but at this point all they have is a letter from the lender and I don't believe they have even sent financials in yet so there shouldn't be any reason why the lender won't recommend it to them if they qualify. 

It is the cost of doing business, and in this case, location does matter for an owner occupant.It is interesting how the timing here is critical, between the letter of intent, the purchase and sale agreement, the mortgage lender's appraisal, the petition, the physical inspection, etc.

I have found an opportunity to buy a small cabin w/ cash in AK where I proposed buying a property from a family through a hand-written letter. 

She recently made a new payment of $800 and I received a letter saying that they received her payment but she needs to pay 4,440 by the 10th or they would proceed with lien foreclosure and eviction.

Or should I ask for interest only payments and then a balloon payment when I refinance in 12 months?

We also sent one agent a copy of our "congratulations on your $xxx HELOC" letter.  

I would probably include the following relevant/tailored info. on you: resume, short cover letter/explanation, financial info.