The rest of the balance of your 401k continues to grow tax-deferred.

Also, neither is well suited for repeated flipping as it is considered a business and subject to taxation inside of an IRA on UBTI.A Rollover as Business Startup (ROBS) plan would allow you to use tax-deferred retirement savings as a shareholder of your personal flipping business. 

I look for buildings with a significant amounts of deferred maintenance.

Stabilized rents, made some repairs on some of the deferred maintenance, and hired killer PM to manage the property.

We have great credit and great income and have the 20% down payment ready to goAs for the offer I'd like to do the 3 option method that I've heard Brandon talk about, so my thoughts were to come in at $17,000 with a conventional loan offer and then throw in a seller financing deal ($21,000 purchase price, $150/month and paid in full in 3 years) and a 3rd option of a deferred down payment?

A lot of these are 100yr old frame buildings that have 6 figures of repairs and deferred maintenance. 

On #3 - I have another rental that would have to be 1031 exchanged so we can defer capital gains.

Seems that any deferred maintenance would tank this pretty quickly...

Then you 1031 exchange and defer the rest of the gain and all of the depreciation recap.Truly a win win scenario for you!

He may be able to present options that allow you to defer capital gains taxes that you hadn't thought of.