I have started using a spreadsheet but I would like something that makes it easier to keep track of when I have sent the owners a letter or postcard etc; also to attach a picture of the property and some pdf's of county record documents.

We were able to overcome it by providing proof that we paid, and were completely responsible for the loan and had recorded documentation to prove it (letter to lender attached below -  (side note this was for a VA loan so we used an agreement for sale in this case). 

Adding interest rates to the mix makes penciling out deals increasingly tricky.

I would start by ensuring you have your forms, form letters, website, and everything ready to hit the ground running.

IRS private letter ruling PLR-157111-06.  

Similarities to self-management but there is so much more to learn especially if you want to grow your portfolio and add investors, or other landlords into the mix.

Most builders require you to provide a Pre-approval letter or Loan commitment from the bank.

You can pivot based off the neighborhoods whether you want more appreciating deals or better cash flow, I have a mixed portfolio worth about 2.5m.Let's chat i'd love to help guide you and possibly serve you with your real estate needs.

Would a letter from the neighbor suffice? 

If they give you a proof of funds letter without a full application and credit review burn it.