Creative Deal--How big of a balloon payment can I make?

[Jacob Stevenson]

Looking at a portfolio purchase.  180k purchase price, 20k down, balloon after 5 years.  Payments based on 15 year amortization with 6% interest.  

My question, at 5 year mark, if the properties appreciate at 4%, I should be able to get $153,000 with 70% LTV. I would have a balloon payment of $123,000. Is that enough spread to be comfortable? I've never done a balloon payment before and it scares the heck out of me.

Any advice would be greatly appreciated!