IRS private letter ruling PLR-157111-06.  

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

Note and lien filed by LLC at 0% interest, 12 month term, balloon payment = purchase+rehab - Correct.  

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

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.

@Taylor CookBe sure to get an estoppel letter signed by the tenants and seller stating the current amount of the security deposit and any other pertinent facts not recorded in the lease.

Establish relationships with brokers specializing in multi-family properties, send letters to property owners, and use online platforms like LoopNet, Crexi, and CoStar.

I typically recommend beginning with a prequalification letter so you can have a solid understanding of your purchase power in the U.S., which will help steer you into the right markets/areas for investing.

And assuming that loan does not have a "due at sale" clause on there that would give you a massive balloon payment.