Vendors can do it because we spread the costs among thousands of customers. 

Something else to consider is the type of customers this type of business will draw.

About two months after the payoff, I received another offer from the same lender, offering $200,000 at a reduced rate of interest since I was a ‘preferred’ customer.

No business will last long if they automatically assume their customers can not afford to pay and simply allow them to walk away.

I'm going to make it really custom to the group that will be there. 

They are usually always willing to help point you towards their better/more reputable customers because they get more business from the recommendation. 

As long as proper expectations have been set and it is not an emergency, getting there to do this "preliminary evaluation" within 48 hours is still excellent customer service. 

There's no real 'fair' way to truly separately meter the natural gas used for the different units, unless you get into rabbit hole land of re-inventing a wheel and a series of sensors measuring heat and air flow within separate ducts, on your (customer) side.I'll comment on each option individually and your decision will be numbers driven. 

(interior at hot water heater)$55 + 57 for the meter(S) and 900 for the 3g data logger, which is 20-30 per months for 3g service. 150 setup fee for customer billing management and a kick back from the tenant of 5-10 for convenience fees.

Look at the apartments in the area of your condo, these apartments are going to be your direct competition, you'll need to offer something they aren't offering to win the customer between the two of you.