We also own a single-family home with a detached garage and a separate lot that is currently secured with the mortgage of the single-family home (we've owned this for 10 months).

Cash flow and taxable income are separate calculations.

From my point of view you need to separate work and investing by giving them deadlines and sticking to them.

Many of the above comments are very spot-on.Not sure if this comment will help, but maybe there's a way to get the best of both worlds if you can build this studio separate from the building and split the lot? 

Depreciation must be calculated separately for the carryover basis and the excess basis.

A completely separate issue you hint at is whether you can have tax benefits from an STR that you also use for yourself sometimes.

For example, during my application they rejected it the first time because they required that all of my points be SEPARATED by all the different brokers I worked under (signed off separately in terms of how many points I earned under which broker) 2.

If this isn't a separate dwelling unit you can't take losses from the rooms / space you are renting and use them to offset non-passive income (Section 280A of the tax code)Rental expenses are limited to the amount of your rental income and the balance of rental expenses is carried forward. 

You may use one account for multiple properties or separate accounts for each property - up to you.

It has separate gas, electric, two hot water heaters, etc.