Tim,An umbrella policy is a policy that provides additional coverage if the limits of the underlying policy (home, auto, rental dwelling fire, boat, etc.) are exhausted by a claim. 

Tenant further agrees that Landlord may continue charging rent until a replacement Tenant takes over or the security deposit is exhausted, whichever occurs first."

DSCR should only be used once you've exhausted your conventional and local bank sources.  10% and 2 points sounds more like hard money than a long term DSCR loan.

Mastering little crap like hanging blinds, ceiling /exhaust fans, light fixtures, switches and receptacles, closet doors, doors, screens, screen doors, patio doors, lockset changing and unsticking, smoke alarms, appliances, paint, trim, wall repair, cleaning, etc are the most common needs. 

Maybe having a slightly larger amount of reserves than normal to be able to withstand any sort of downturn?

House hack a multi family property first and then either do it again using FHA or conventional financing, but DSCR should only be used once you've exhausted ALL of your conventional and government options.

If the item needs to be replaced before the depreciation schedule is exhausted, there should be almost no residual value to be expensed anyway.For these items there is no additional depreciation to be gained and the total depreciation expense is reduced if the item lasts longer than planned.

I won't go too technical, but just so you know, the heat exchanger is a "metal box" that contains the gas burner and exhaust fumes inside the metal box. 

Here you are attempting to prove you can withstand a substantial loss in a risky investment.

I can say the last three and half months have been quite exhausting juggling this project, family, and work --- so we hope all the time and expense will pay off.