How many times can you do that with a contractor before it becomes exhaustive on the investors part?

The system in use had pvc pipes coming from the attic to provide air for each room...

The scope of work includes new kitchens, new baths, flooring, paint, and repairing water damage/burst pipes. 

Some issues like egress windows or exposed pipes can be fixed and you need quotes for this.

I'd be up at night worried about water leaking from a faucet, all those pipes just waiting to break, that old window that is about to start leaking, or pests getting in, or mold, or appliances breaking, or tenants causing damage, losing their job or getting divorced or dying, or a tree falling on the house or sewage backing up into the house or any number of unexpected and expensive things that happen at the least opportune times.

I'm currently new and gathering information so there is nothing in the pipe line just yet but i'm looking at single family homes first.

I can eat a $10k-$20k unforeseen expense (Contamination, burst pipes; etc etc) when my profit is $100k+.

Other non-code enforcement issues I look for when doing inspections on my own: change air filter, check to make sure toilets are not running, run water in sinks and check drain pipes for leaks, check for signs of unauthorized pets, check to make sure all windows operate, check all GFCI outlets with a tester and make sure they reset. 

If it is not their fault (ie a tree root has grown through the sewer pipe which is why the toilet keeps backing up or something like that) then I would probably get the problem fixed after the 3rd time it happened.

I can’t remember the ridiculous numbers exactly but it built a 16-17 story building in just a couple weeks or less.As a very forward preparing GC, we are getting ready and prepared to be sensor installers (plumbing pipes, wood rot detection, foundation shift, etc etc.).