I am located in the north shore area of MA and got my two duplexes through house hacking but always will to share my experiences! 

Leave it to the experts is my recommendation on drafting all the documents after the terms are agreed too.

The first one is a 3 bedroom 1 bath house on 1.67 acres.

The house will be used as a short term rental.   

These properties are older and generally on the low $ end so there is not much room based on ARVs to replace entire system but wondering if leaving it in would scare away buyers.

Moisture in ceiling; subfloor damage.Moisture in ceiling; staining and previous repairs.Moisture in baseboard and floor.Moisture in ceiling; staining.Moisture in ceiling.Roof replacement; address moisture and leaks.Exterior inspection; identify and fix moisture sources.Fix moisture damage.Electrical system overhaul; ensure safety and compliance.Temporary housing costs for tenants during repairs.

They claim to have owned four rental properties and a large house which they sold before coming here.

Podcasters that does house walk throughs will sometimes say, "if this Floorplan isn't available in your city/state"  blah blah blah.

For example, I would need a new loan from a bank for the remaining $550,000 after the 4 years or would refinance the house for the $550,000, correct? 

I have bought and sold over 1,000 properties for my own inventory, and did Bigger Pockets Podcast #82, and have spoken coast to coast from Manhattan to San Francisco on real estate topics, and wrote a book on my experiences.So I can't say I did it all on SFH, but renting houses has been a big part of my real estate investments since I first started investing.