I was a painting contractor in another life, so while I can't say much about plumbing I can say that if you have a good and ethical contractor, he will tell you if and when the plumbing may need to be replaced or upgraded. 

If you don't upgrade them.

I want to apply the BRRR strategy to this property but am clueless when it comes to upgrading properties and adding value to a home.

So now you've gone thru the "cosmetics" Kitchen remodel/bath remodel/opening up the floor (and don't forget the cost of the "supporting beams") , new flooring, paint, smooth ceilings; don't neglect the structural aspect and exterior - electrical upgrade?

The one with the broken relationship wants a healed relationship.

The backyard has some broken cement surface (about half) and some dirt.

There are a few and minor things that needs repairs since they maintained the house pretty well(second family to own it), just needs some upgrades.

I am resigned to be patient and to look for properties that can be upgraded for increased value.  

What the expectations of tenants are as far as finishes and what upgrades will bring higher rents come with experience and learning your market.

Before I go look at a new prospective property, I already have a "rough" estimate of rehabs assuming it needs the majority of what the properties I buy needs - floors, kitchen/baths, HVAC, electrical upgrades, etc.