Since it is always better to offset the cost of utilities to the tenants, and because the oil tank may need replacing soon, I was thinking about converting the property's heating to gas and installing a boiler for each unit.

You'll find a lot of great people (and a few sharks) in the Baltimore Real Estate Investing community.

Omg, btwn Rapidly changing rental laws & impossible to find good people for cleaning & maintenance & exorbitantly high property taxes & power bills & septic tank repairs...This is why every Poconos thread on here turns into a bunch of people complaining!

Broken strings or any damage resulting from a pet.Dirty window and door screens.Torn or missing screens, bent frames, etc.Sticky or worn window mechanicalsBroken windows, frames or abuse resulting in poor function.Loose, worn or inoperable faucet handleBroken, scratched, damaged or missing faucet handleRunning toiletBroken toilet seat, tank top, handle or chipped, cracked or damaged toilet bowl, tank or seat.Musty odorUrine or pet odor throughout unitCloset bi-fold door off track or needing adjustmentDamaged or missing bi-fold door, knob, track resulting in poor function.Old, expired, or non-functioning smoke or CO detector (not resulting from damage)Missing or detached smoke detector or CO detector or missing batteriesNon-functioning light or electrical fixtureMissing, burnt out, or incorrect style light bulbs or damage to a fixture resulting in non-function.Dry, brown lawn or landscaping (not resulting from neglect or failure to water or tampering with irrigation or timer)Lawn with pet urine spots, dead areas, excessive weeds, lack of irrigation as a result of neglect or tampering with irrigation or timer settings.

Propane tank will be on the outside and professionally installed by watsons.I'm looking for some opinions on whether this a good idea or not.

You have to account for the maintenance and replacement of additional furnaces, water tanks, heaters, ac etc. 

I bet the fed keeps rates where they are for at least a year, unless the economy tanks for some reason.

Leave furnaces, hot water tanks for last. 

I've kept up with improvements including new driveway, new doors, rebuilt balcony, removed asbestos tiles in basement, laid tile in the kitchen, re-did hardwood floors, repair leaks in basement, new hot water tanks, new/updated electrical panels.

I have the drain hose connected and going straight into a floor drain, so I don't have to worry about tank filling and needing emptied.