My Realtor is asking my to provide a proof of funds letter before submitting my offer but I have no clue how to get one. 

With my structure, I'm the one sending out 50k letters a month and bringing in the leads, so there is no reason to split 50%.

The terms I am looking at are basically 10% interest only loan with no prepayment penalty and a 12 month balloon payment.

If you mean it will be a 5-10 year balloon payment mortgage about 1/2point higher than a residential., then no that is not necessary.

If they are willing to work with you they should be willing to give you a letter of good funds that you can use when putting in offers.  

A basic letter will accompany each resident's renewal notice 90 days before their lease expire.

After a visit to the property and a conversation to the owner I searched BP for some sample follow up letters to tenants concerning HOA violations.

Most of the time we send letters that say "Hey, nothing is changing other than who you make the checks out to, and where you send those checks!"

I guess this would be considering a wrap around mortgage since I'd try to keep paying on my mortgage - though I do have the ability to cover if they were to activate that rare due on sale clause.So my questions are for anyone who has had experience in structuring seller financing deals:1) My initial thought would be to structure it to parallel my own ARM to keep her payments low for 5 years (close to what she's been doing for rent) and have a balloon payment in 2020.2) What kind of interest rates are usually charged in this situation?

When they finally understood they wrote a letter to the mortgage company responsible for the error.