He is paying the loan back with post-tax dollars, so there is the hidden cost of whatever his tax rate is.The better option would be for him to rollover all or part of that old employer 401k to a self directed IRA.  

From there, they will likely deliver those documents to you, help you setup a bank account for the trust, and support you in any transfers or rollovers of existing retirement funds into the new Solo 401k.

The business sets up a profit sharing plan or 401k that you can rollover tax-deferred retirement savings into such as from an IRA or old 401k.  

I do have a partner that wants to buy more SFH's and I on my own want to roll over my IRA to a SDIRA and do some flips in the area.

With the IRS approved Solo 401(k) Plan, roll over your existing IRA or 401(k) plan funds tax-free into a new Solo 401(k) Plan and use those funds to make tax-deferred investments, such as real estate, while also gaining the ability to borrow up to $50,000 as well as make annual plan contributions up to $59,000 – almost 10 times the amount of an IRA."

@Skip GilliamWhile not for everybody, you may want to look at the Rollover as Business Start up (ROBS) if you are looking to quit your corporate job.

Or for the vehicle have to remain business use only 2) Does the 100% vehicle deduction roll over?

There's been difficulties setting up my checking account at the local bank and rollover of my funds from Fidelity.

Fortunately Canadians are smart enough not to make RICO level mortgage origination fraud legal (unlike your southern neighbors here in the US) so a collapse brought on by mortgage rates resetting on borrowers who had no business getting a mortgage in the first place is very unlikely.On the other hand with mortgage rates below 3% and most Canadian mortgages being short term (compared to a 30 year in the US at least) if rates rose significantly a lot of folks might have a hard time affording the new payment when the loan was due to roll over.

I really did not think about the rollover availability.