If I have something small (backed up plumbing, outlet not working, etc) I don't call the warranty company.

Plumbing and HVAC may sometimes make weird sounds in the walls.

I'll be the first to say that I am a bit scared especially of the electrical or plumbing or just being taken advantage by a contractor. 

I ended up putting around 30k into the repairs, doing 90% of the work myself except for what I had to hire out to a crew or a professional (roofing, some electrical, some plumbing).

Since this is a bigger project than we have done before we plan on hiring a contractor to do the major work; demo, framing, electrical, plumbing, and sheet rock.

One thing which is often neglected is the plumbing.

I own a construction company and do most work myself outside of plumbing, electrical, HVAC, roofing, and flooring because I've found some great subs.

I had 11 of these and good systems in place but still had 1-2 evictions a year and 3-4 big things that were normal annoyances like plumbing leaks, damages from hurricanes, or some vandalism.

Roof, HVAC, plumbing, electrical, kitchen, bath, walls, floors, foundation, ceilings, etc.I have found that what costs is when the entire house needs to be replumbed or  there is no heating and air, or the roof is bad, or the floors are falling in,  rather than the cost for a bedroom rehab.Then again, I buy foreclosures and they tend to be worse than regular housing. 

@J TorresAgreed that having both properties on separate meters is a good strategy, specially if you are doing the plumbing anyways.