That would seed the SDIRA with more than the $6000 per year + avoid a taxable event.

(Talk to an attornet) If he sold you the $165k property for $1000, and you later sold it for $200k, you would show a capital gains taxable profit for $199k, as opposed to buying it for 165 and selling it for 200 with only 35k being taxable profit.

Using a traditional solo 401k ira, then i would be able to reduce my taxable income by $50,000.

If you bought it as your primary and have lived in it for at least 2 years, there is no taxable gain, up to $250k single/$500k married/joint return...irs section 121.

So, shouldn't be anything taxable, etc. 

Plus, its non-taxable per IRS rules.

In addition, if the child owns part of the property as their primary residence they would be able to take advantage of the $250,000/$500,000 tax free exclusion on the portion of their taxable gain when they sell. 

How much money you borrow on a property, or how much equity/cash you walk away with after a sale have No bearing on your taxable capital gain.

Selling the property in this manner is a taxable event, although probably not much in taxes would be owed.

But your primary is a bad idea….1) you’d create taxable income with the rent from your primary2) improvements are capitalized /depreciated3) you’d lose your homestead exemption/protection4) you likely lose your section 121 exclusion