OP here! We're now a couple months into ownership, and staring down the end of a 2016 tax year with all sorts of new awesomeness in it, so thought I'd update this thread for fun and posterity... and so folks can shout at me (kindly!) if any of my logic seems unsound.
After doing more reading of IRS materials about figuring basis on real estate, I've gotten more specific about our basis in the property. I combed through our final purchase paperwork to pick out title & settlement charges, legal fees, and recording fees -- added to the purchase price, our basis in the property overall comes to $825,347. (Yes, as previously noted -- I know that's a higher property price than frequently considered normal around here...)
Based on the division of floor space per our appraisal, we're allocating 62% of the building for our personal, owner-occupied space and 38% for the rental unit. Total basis for the rental unit is thus $313,632.
Based on the land-vs-building percentages assigned by the assessor's office, the rental unit basis breaks out as $89,094 for the land and $224,538 for the building. We'll thus claim $2041 in depreciation in 2016 (3 months) and another $2041 in depreciation in 2044 (3 months)... and $8,165 in depreciation for the 27 years in between.
We've got a bookkeeping system sorted out for rental income and expenses, and I'm feeling pretty confident about tracking that well. For 2016, our rental expenses will exceed rental income by a hair on paper (< $300); in future years, I expect we'll run a small profit (probably a couple of thousand dollars per year). I believe (from my own reading, and from brooklynguy's previous comment) that I can carry this 2016 loss forward and apply it toward a future year in which we have a paper profit on the rental.
We cannot deduct rental income losses from our other (earned wages) income because our AGI is too high (and will be for ~10 years, if all goes as planned) and this type of rental business is considered "passive" even though we, as self-managers, "actively participate."
And then, just for fun, to look hypothetically into the future... let's say that for 30 years, the property appreciates at an average of 2% per year, at which point we sell. Hypothetical sale price in 2046 is $1.4M; assuming some costs of sale, I'm taking that down to a net sale value of $1.316M (assumes 6% cost of sale). Of that, $815,020 counts toward the sale of our owner-occupied unit, leading to a profit over our original owner-occupied basis of about $304K -- upon which no income taxes are due (under $500K profit for a married couple filing jointly). However, we'll also have profited on the sale of the rental unit, to the tune of $186,448. We'll pay a 15% capital gains tax on that (just shy of $28K), and then a 25% depreciation recapture tax on the $224,538 building basis we'll have depreciated between 2016 and 2044... so that's a nice tax bill of a little over $56K. All told, we're looking at a tax bill at sale of over $84K in the far-off future of 2046. Unless there's some sort of double indemnity/tax overlap thing here that I don't understand? It seems to me that some of these dollars are effectively getting taxed twice, once as a capital gain and again as depreciation recapture...
Thanks for providing a space for me to think this out in pixels... I find this fascinating, but I can't get anyone else to geek out with me.