He was the proverbial tired LL whose wife was nagging him to unload the 3 unit after spending a lot of money on it for mechanical.

I disagree on needing 20k saved, I once closed on a property by trading some mechanic tools that I found in another house.

I am a mechanical engineer with overlapping experience in project management and construction.

In order to put a mechanic lien on a property does a contract need to be written up?

Mike Armour with Blue Ridge Mechanical.

It depends on the insurance company and rates you are going for.For example some insurance companies only insure brick buildings in certain areas built within the last 20 years.The reasoning is you get ultra low rates by having a low risk pool of properties.Insurance companies have told me with buildings 30 years or older some do not like to insure unless all mechanicals,plumbing,electrical has been replaced.The reason is statistics shows a high volume of claims happen after that age from things wearing out.With 4 units or less many just get the cheaper fire and dwelling coverage instead of a commercial policy.If the premium low rate insurers won't touch you there are companies who will give the policy to more properties deemed high risk but the policy of course will be higher and usually the deductible is too.

Alternatively, if you have to be a guy who is involved with the mechanics of the operation, find a trusted GC in an area that isn't so speculative.

It would not be a complete waste of time to get yourself familiar with the structural, electrical, plumbing and mechanical components of a home.

I've got a fourplex which I purchased in 2010 and have pretty much completely renovated each unit and replaced all the major mechanicals (4 water heaters and hvac furnaces). 

Or a reliable mechanical door lock they use?