The age, type, and condition of the plumbing is a significant factor in whether I'll buy a property, and how much I'm willing to pay.Electrical.

Hi Michael,It is great that you are doing this together, I read some great tips on here, something I wanted to add:I have been checking a lot of 2-4 units, in the past it was not easy to find them in good areas.During COVID, a lot of investors decided to build these types of units which is great, but not all builders are great, I had a client, he purchased 2 duplexes in the same area, we had some pricy maintenance issues, one was with the plumbing.

Water heaters, furnace, plumbing leaks, replacing a roof, replacing the main water line, tree trimming, microwave replacement, etc. $20-25K would be awesome but you can likely get by depending on condition for $10-15K. 

Bad publicity and ratings will cost them a lot more than a plumbing repair

I also redid all the plumbing, electrical, and painted the entire place.

Finding the property, negotiating, finding and managing any subs for work he would not do (such as plumbing and electric), purchasing materials, doing quite a bit of the labor. 

A contractor can help yes when it comes to looking at it and telling you how much or what you be looking at if you want to upgrade or fix something visible but you need the inspector to check out the roof AC and plumbing thoroughly despite what it looks like in person I’ve seen mini jacked up ceilings.

Upgraded the roof, plumbing, electrical, waterheater and windows.

I would also check references and make sure the installer is licensed and insured.Roofing has more variables-disappointments- than even plumbing and you want it done right the first time.

Ag well + domestic well, or just one well and does that require softener (component inspection and well inspection).