Hey @Paul O'Connor
Congrats on the opportunity first of all. There are some really good due diligence lists out there that you could tap into. They will be REALLY comprehensive and you likely won't have to follow everything in there, but I always think it's rather to start with too much and widdle it down. Here is a high level example:
https://northeastpcg.com/blog/...
To answer your questions above specifically:
1) Yes, RO systems exist for well water. There should be a lot of companies in your area that offer this service. Have someone come out and take a look, it should be relatively inexpensive to complete.
2) This is up to you and your leases. Usually on commercial properties you have CAM (common area maintenance) expenses which are fully paid proportionately by the tenants (based on square footage). However, mixed with multifamily you will likely want to allocate some of this expense either as a fee to the residential tenants, or more likely, an expense to the building/company itself.
3) It depends on how your utilities are set up - do you have separate electric/water/gas meters? If so, then I always like to have tenants pay for utilities. What is typically more common (not always though) in multifamily is that some utilities will be included because they won't be separately metered. However, I would always ensure the commercial tenants are paying for their utilities. If it isn't separately metered for them, come up with some type of distribution of charges that you have in the lease. One important note - the common area utilities can be charged back to the commercial tenants through the CAM, though again you may need to pay a portion of these CAM expenses for the residential tenants.
4) I have never seen a municipality that didn't have a fee associated with sewage. It should be easy enough to figure out though, just call the municipality and they'll be able to answer that for you.
5) Again, usually there is a fee for this, or it is included in your property taxes. But when dealing with commercial/multifamily property, you almost always have to have separate waste disposal. Again, a call to the municipality will quickly clear that up for you.
For due diligence, like I said there are some really comprehensive documents out there. But at a high level, I want to know property taxes, insurance, and utilities historically (and most importantly, VERIFY THESE YOURSELF). Historic vacancy rates, rental rates (are they increasing, staying the same, etc.), and issues with tenants. It's also really important to know the maintenance status of the building. Has it been well maintained, or are the owners trying to pinch pennies everywhere - which will now become your problem? What kind of plumbing and electrical exists? How is the roof? Is it wood building, brick, or concrete? What does the boiler/hot water/furnace look like? Have they been maintained? Do they need to be replaced relatively soon?
Usually, on this type of property, you're going to need an appraisal and an inspection. But even if those aren't required, I'd always recommend getting the inspection done. It can help you stay away from a bad deal. Good luck with everything!