No, you can not wire 1 HW heater to 2 different panels, even if you did you still wouldn't know who was using how much power.

Our underwriting criteria varies on the kind of deal, but for something like this I look carefully at the systems and major costs that you mentioned: Age, style, and type of roofAge of furnace or other heating mechanismsCondition and material of plumbingElectrical panels - what type and is there sufficient loadFoundation conditionOngoing maintenance concerns - trees!

One thing to note - it is asbestos, so taking it off causes a hazmat situation, which you are not supposed to do yourself (at least in my state).Cost to deal with both of these things will vary based on the property, but in general, updating a panel and service is $2,500-$3,500ish. 

If you are getting a duplex worth 700K for 15K then everything is irrelevant because I can get you a couple nice heating units and a couple hot water heaters with a sweet set of 6 panel doors and some vanities still leaving 6 figure profits. 

Can you do a walk-though and recognize foundation issues, truss issues, sewer line issues, electrical panel issues, etc?

I am in Oregon and looking for a electrician to replace an old electric panel. 

And also, I have 2 100 amp panels - one for each unit, would this need to be upgraded? 

We added a second kitchen in the basement, a few cosmetic items, new landscaping, central a/c, new electrical panel to accommodate the extra kitchen, and ran additional laundry upstairs.What was the outcome?

I travel most weeks for work in a normal year, so this was a nights and weekends project, but I'm proud to say I did 99% of the work myself, with the exception of the new electrical panel and a couple other specialty projects.

My father built panels and then assembled a garage with assistance.