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. 

I would aim lower for a first play.

In that case, you need to measure the likelihood of getting another tenant at your over market price vs. getting one at market rates, if that is what the tenant wants to pay.

Otherwise, I think you're wise to measure the return on investment associated with renovating your units.

Take your measurements and price around.

Aim to establish contacts to help you (contractor, agent, PM, etc) within next 3 months. search for a home for 3-6 months (that meet your risk level) and close.  

We aim for good cash flow and get it.

I aim for top of the market, but my place near the city park gets higher rents than the one near the industrial strip.

Real estate adds responsibilities, and you should move forward cautiously, measuring those responsibilities against your income.

My aim is not to waste anyones valuable time but simply to gain experience within the field.