These tax deductions do not require you to become a real estate professional.

I can deduct the interest, but it gets added it B and C vs A?

Repairs made while the property is your primary residence are not deductible, but improvements can increase your cost basis, reducing future capital gains tax when you sell.

I'm just here to note that an LLC does not offer a single tax benefit, nor does it allow any deductions that aren't allowed without an LLC. 

Bear in mind that the fiscal treatment of the two options in Mexico is different (withholding tax on the gross income with the fideicomiso vs cost deductions with the corporation).

Yes, you can deduct the 8 days rent from the security deposit.

This would allow them to fully defer their taxes if that was their goal. 

This is due to bonus depreciation which allows taxpayers to deduct 40% of qualifying property costs in the first year, in addition to regular depreciation for new construction and improvement.

Interest income is interest income, unless you decided to roll some of the current cash into a self directed IRA at which point your interest income would be deferred for a later time and allow your funds to grow tax free.

It's definitely not your fault that the kid allowed the sink to overflow.It's not the tenants responsibility to inspect caulk.