updated all plumbing in home.

Plumbing: separate water heaters, what size, what year?

They pulled an addition permit, electrical, HVAC, plumbing. 

How much are the upgrades, are they aesthetic or roofing, plumbing and electrical? 

I worked as a General Contractor for years, and can do any/all repair and maintenance work short of plumbing and electric (I'm just not licensed for them)5.

Our labor on avg is under 2k for each of those if there’s no electrical or plumbing to be rerouted.

I plan on walking the property with a contractor before placing an offer with the intent of scoping out the needed work on electrical, plumbing, roofing, and the foundation, which would be the big ticket items, along with all other work.

They may have to move some plumbing connections around but it shouldn't be much more than a regular water tank.I understand that some systems have a water heating system separate from the hot water. 

Few weeks back I asked them if they had any issues with their property including plumbing and we found a leak under the kitchen sink that apparently was there for a while (tenant never reported it to me) and now I am arranging services to make the plumbing repair. 

Moisture / water / mold, knob & tube wiring, foundation issues, ancient plumbing, rust on the breaker panels, termite tunnels, powder post beetle damage, cedar post supports, improper footings, temporary lally columns, etc.As to writing an offer, that's a sensible and common approach.