That also includes self-directed IRA’s as well as standard IRAs.

You could do 2019 taxes per their standards and if you and your accountant see's fit possibly amend 2018.  

If so, no matter what your lender is telling you otherwise, the appraisal is going to be done to FNMA standards, unless the appraiser is an idiot (and that happens all too often too).And just because there are somewhere around 10 different ways to approach value on the 1025 Small Income Report, the appraiser only uses one, because FNMA only recognizes and loans according to one - the reconciliation of the sales comparison approach.

@Dylan Eggers - Commerce City has had insane returns the past 5 years (the house values had doubled) but in 2019, it seemed like the Suncor facility was making people sick, so I agree with Craig about avoiding that area. https://www.thedenverchannel.com/news/local-news/regulators-hit-suncor-energy-oil-refinery-in-commerce-city-with-over-100-air-pollution-violationsThat said, I love Thornton and Westminster.

But they provide standard documents for all businesses, whether you are a florist, a manufacturer, or a real estate holding company.

Court searches, with local tax certificate for village or City taxes, if any (collectively the "Abstract" and (ii) an instrument survey map, certified and prepared to meet the Standards of the (locality) Bar Association and Buyer's mortgage lender, if any (the "Survey").

In short:One partner is your 401k and the other partner is the other investor.This could be accomplished via an LLC (i.e. one member is your 401k and the other member is the other investor).This means that partnership will have to file partnership tax returns (1065 at the federal level) and issue k-1's to the partners (e.g. one would be issued to your 401k under the ein of the 401k).The terms of the agreement (including the payment flows you mention) would be negotiated and documented in the operating agreement where you sign as the trustee of the 401k.The standard rules regarding investing in real estate apply (i.e. you can't use the property for personal use, you can't work on the property, etc.). 

Also, the project could actually take longer than the 1st house if the contractor adds contingency days to the schedule to mitigate the risk of damages  Good luckAs far as the payments go, there are 2 standard billing practices, percentage of completion which is by far the most common or you include drawers in the construction schedule based on completion on milestones.

For a standard rehab/flip loan, does the loan product support a pure "asset based" approach? 

Once you've purchased the duplex, screening tenants properly and never veering from your standards is the key to making it work.