Hi Matthew,4 furnaces might require re-ducting because older systems share ducts sealed into walls throughout the house.Not such a problem on the first floor, but as you go up it gets complicated.And since it's a propane area, if the residents are going to pay for the propane, individual tanks would probably be a good idea unless you intend to sub-meter them.And 4 mini-splits might require more amperage than the house currently has.Plus if you have any common areas that need heat, that means a 5th heat source.If I were looking to buy something like this, I'd prefer it to have furnaces (and separated electrical panels for each unit) vs a mini-split set-up. 

was panel upgradedInside- first thing im looking at is layout.

Be prepared for cast iron sewer lines, foundation repairs and probably electrical panel swaps, along with the usual cosmetic updates. 

CB main panel unlabeled.3.

I am putting GFCI outlets at the head of each circuit and I updated the panel with new guts.You can use 3 prong outlets on a 2 wire system with GFCI's if you use the little stickers that come with the GFCI outlets.

My passion is to obtain properties for renting, both residential and commercial, and apply solar panels to all of them to help shift our modern world to a greener future.

I just got back from Raleigh NC where I was invited to speak on a panel. 4 hours each way.

You have to install sprinklers, rain barrels, and solar panels.  

-over-fused, poorly labelled electrical panel. several ungrounded outlets.

Any existing fuse panels will likely need to be upgraded to circuit breakers.Insulation is generally poor.