It is slab with a small basement in one section for the mechanicals.

Depending on what mechanicals are there multiply that by at least 4.

I read in different groups and forums the posts of locating notes & the mechanics of the note, however my questions are more basic than that - what infrastructure should I have in place (such as I've heard that I need an 800# & that then I don't); what type of business entity as I start out; software and hardware needed; to what services should I subscribe or be looking at as I grow?

Very rarely do you ever see a renovator/builder who doesn't sub out mechanical and roofing, at the very least.

I suppose I should just assume the mechanicals will need lots of attention and adjust my offer accordingly since I will not be turning on the utilities and neither will the seller.

The seller can't take all the cash flow over the years and then dump delayed repairs on you that will kill your returns for years and get a market premium price.Pay special attention to all the mechanicals, condition of the kitchens and baths etc. as those take a ton of money to fix and repair.

This is an invest property with the emphasis on INVESTMENT.

Some of the other buildings in the area might have low vacancy due to location,rent prices,amenities,etc.4.200k in reno with 5k per unit is light.Unless these need just carpet and paint,resurface of the parking lot,and updating of mechanicals the cost is likely to be much more than that.What year was the property built??

Before you rent out the property be sure and replace anything that may go out in the near future...water heater, HVAC, garbage disposal, faucets, toilet mechanisms, supply lines to toilets and faucets, dishwasher, etc. 

Seriously, the siren song of half price mechanicals is seductive, but if it's too good to be good it usually is.