Investing this way:Avoids the single family residence mortgage interest cap to take advantage of significant tax interest deductions.Lets you be on the winning side of the age-old argument that "everyone needs somewhere to live".Lets you take advantage of expensing all of your capital expenditures immediately when they are incurred to offset your normal income taxes from your day job and potentially pay no taxes at all in a given year.This was not entirely possible in 2017 because any capital expenditures had to be depreciated over a 27.5 year period for multi-family properties vs expensing immediately.Have an effective maximum tax rate on your investment income of 29.6% if you do end up having any income that isn't offset by the capital you put up to do renovations on the multi-family units.

I'm also in a position to cover any capital expenditures for the foreseeable future, which would most likely be the HVAC, since the roof is 6 years old.I'm also carrying a mortgage on my current residence for $800/mo. if that would factor into anything.I'm self managing the property, to get some experience and saving on PM fees. 

Oh, one other question re capital expenditures: how do you calculate for those?

Because a four plex is a rental...always a rental, you may find a good many as I did...in rough shape, needed a lot of capital expenditure (CapEx) once you acquire the building, even if the price is good.  

Is a capital expenditure deduction of 30% a fair estimation of any "extra" expenses I might miss in my calculations?

That's 2.6% gross return before taking off all expenditures.

That being said, many investors mix capital expenditures with expenses for certain tax strategies, so understand before your jaw hits the floor that many T12s will be wildly inaccurate. 

The new construction is obviously not going to need any repairs, better not need any capital expenditures (except a fridge if the new house doesn't come with one, but Best Buy offers extended warranties if you buy one).

The goal would be to have positive cash flow at the end of the month after you have paid your mortgage, cap expenditures, property Mgt ect.

I think most people would also try to set aside a portion of the rent for possible repairs, capital expenditures, vacancies and property management.