Electrical on 1, and Plumbing on the other.

He hires out the foundation, framing, siding, roofing, electrical and painting.He and his buddy do all/most of the carpentry and plumbing inside.

Expect to have to re-wire and plumb everything to current code which sometimes can be more expensive than the rehab itself in order to get a new certificate of occupancy. 

Regulating noise, garbage collection, colors that can be used for homes in the area, rules around parking, rules for landscaping, and allows for a process for dealing with problem neighbors.

Considering a duplex that is 53 years old, has not had plumbing or electric upgrade.

You would need to contact your city/county to find out what the regulations are--they may require inspections, etc. 

The only way tenants can disagree with a rent increase in non regulated states is to move. 

That is what drives rents and prices, either with or without rent control ... the free market supply and demand is what drives things in the long haul one way or another, though regulations may distort the market in the short run.

That will teach you about the regulations but it won't teach you about being a good lender.  

With 20/20 hindsight regulators and plaintiff's attorneys paint targets on these individuals through rescission rights or other legal techniques-They train sponsors to source money through other active investors which inevitably leads to squabbling and a loss of control.