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.

.), two bathrooms, added a bathroom, fully redid the kitchen, refinished the hardwoods, paint, baseboard, trim, redid all of the plumbing in the house (above and below ground), water proofed the basement (internal/external french drains and sump pumps, and did all of the landscaping (mulch, new sod, removal of trees, etc.)

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.

The lenders know odds can be higher the tenant goes dark and the lender wants to know the borrower can keep paying on a vacant property and have enough money to pay all the fees involved to lease it back up.So in the past (FASB) Financial Accounting Standards Bureau the tenant only had to book a partial primary  term lease value for their debt load.

Unfortunately, I don't know about the Vancouver, BC market or international investing

I guess this is the same issue as hiding a key under a rock (people can make copies and/or know where your keys are), or using a standard key pad that is cumbersome in terms of changing combo after every stay.

This can end up costing a new tenant over $3k to move into one of our properties if the "standard" 1 months rent security deposits applies.

Set a standard you want to follow and do it. :) Here to help if you needed.