Mileage as Startup Costs and First-Year Deduction Questions

[Lucas Hammer]

So I bought a 2-unit building that I'll be house-hacking while I work on the second unit that I'm living in. I had a few questions come up over the last week while I'm trying to get paperwork together and build my system for keeping everything organized.

1. For anything that benefits both units (yard work, maintenance, etc.), I've been tracking the mileage and I'm assuming that I can deduct half of it on the first unit since the other half is for the unit I'm living in that hasn't been placed in service yet. I'm assuming that the other half of the mileage can be deducted once the second unit has been placed in service, but I can't seem to find a definitive answer on if mileage can be included in start-up costs.

2. Can I deduct the first $5,000 in start-up costs once I do place the second unit into service or does it all get added to the basis and depreciated? There's conflicting evidence on the first $5,000 for a "passive" real estate investment online and I couldn't tell if the $5,000 rule is only in effect for "active" investments.

3. I have a detached garage that needs some repair. It's not dedicated to a single unit and can be used by both units. Would I deduct half of the repairs current year for the first unit and add the rest of the repair amount to the basis of the second unit for once it's been placed in service? Since it isn't a part of either unit and isn't exclusively used, I wasn't sure if I could put that all on one or another unit or if it'd need to be split as well.

Thanks, and hopefully my questions are all coherent enough!