If the trip is mostly personal, then only the expenses directly related to looking at potential investment properties would actually be deductible, which is likely rather minimal - maybe some gas or Uber costs to get there?

The house in question is located in West Milford, NJ and is a 1963 3 bed 2 bath split level on a pretty level .25 acre lot right outside of town center with natural gas but septic, well, etc.

You think 30 years ago we had any idea they'd one day be after gas stoves and lightbulbs?

Upon graduation from college I started work in the oil & gas industry 80+ hours a week.

I'm in a heating climate and a gas boiler would be expected to last 30-40 years at least.

They know the tenant base, median rents of different areas, how much to increase rent each year, ranges of repair costs (ex: tenant calls and says AC isn't working, no hot water, faucet is leaking, the HVAC system goes out).

To manage this, find the average electricity, water, and gas usage in your area.

In these instances, you'd have to check things like flooring, plumbing for leaks, roof for leaks, hot water heater, and heating and air conditioning units. 

I'll go to the county clerks office and get 25 leads for 25 cents a page plus the cost of gas to and from. 100 leads for 300 bucks a month?

The roof is fine until it leaks, decks are fine until they are not, things wear out, line blockages don't happen overnight they most often are buildups over time until the result IS seen overnight.