Hi Dan,
It sounds like you are really doing your homework and being very thorough! I can't speak to some of the estimates, but having bought a very old (1917) 6 unit building in Chicago recently, I can give you my 2 cents on my experiences. I think your estimates for the electrical might be a bit on the lower side. We already had updated panels in our building, but the prior owner did some sloppy work and the electrical was very overloaded in one unit (excuse my ignorance of some of the terminology - you seem to understand it much better!). Anyway, I had to spend close to $1,000 in that unit fixing that situation and installing a lot of new wiring, from someone who was a friend of our handyman - so I know he was not charging us as much as he could have. Our building still has a lot of old wiring behind the walls, which does concern me. Since you are redoing so much of the building, have you considered whether it might make sense to redo all of the electrical? Not sure if that is feasible, but you might want to price it out to see if makes sense to start fresh and not have to worry about cloth wiring, etc. Don't underestimate the cost of installing all of those fixtures, plus emergency lights (which you should put in common areas). They tend to add up.
Plumbing costs can also add up especially if they need to bust through concrete in a basement to assess a problem - I would get your plumber out there (and the electrician for that matter) before you proceed on anything and get the costs more nailed down. I would have the plumber address water heaters - what is there now, what is needed for each unit, cost, etc. Also, where will the laundry be? Is there going to be common laundry in the basement? If so, factor in cost of any plumbing needed plus the cost of commercial machines (can be quite costly).
We had an existing HVAC system so we haven't had to address that or the meters (we had that also in place) but that sounds like a great plan - just not sure about the cost. I would have an HVAC person take a look now rather than waiting until after you proceed further. If the seller is truly interested in selling, they might consider allowing you to get in with these people to get a clearer picture on your true costs. The seller of our building was open to it so it never hurts to ask.
Awesome about the roof being replaced. We just had our flat roof replaced and that plus skylights plus gutters amounted to $10,000.00. With roof being replaced, water intrusion from above should not be an issue, but still think about whether water can get into the building some other way. Our broken sidewalk is angled towards the building, allowing water to go towards the foundation. Definitely a bad thing that needs to be addressed sooner rather than later.
I think your rehab per unit estimate of $16,000 sounds reasonable, especially if you plan to do a lot of the work yourself. The large area of the apartments will probably mean each floor will be $1,500.00 $2,000.00 to refinish if you change your mind about doing it yourself and decide to hire professionals. Ours were about $1,200.00 per unit but we have much smaller units with a lot less wood floor. Makes a big difference, though and tenants will love it. New cabinets could be purchased for about $2,000.00-$3,000.00 from a home improvement store. We invested in stone counters for about $1,600.00 - worth it to me with the durability and tenants love it. Maybe something to consider. A stainless appliance package cost us close to $3,000.00 with the 5 year service warranty.
Well, that's my book for the day. Hope something from here will be of use. I am not sure about how the financing situation would work, but others can probably give insight. One thing you need to ask is about the eventual financing situation. With a 6 unit building, you may have to get a commercial loan with the refinancing part. I may be wrong on this, but you will want to ask. With our 6 unit building, a commercial loan was the only option and it can be a rather complicated process. Maybe there is another way for you to pay off the balance of the building? I am fuzzy on this part with your more creative plan, but you should ask a mortgage expert. Good luck to you!
Elizabeth