Flat roof.

Forecasting for the next year says the appreciation is mostly flat, perhaps a tiny increase of a few thousand dollars.  

What would be the best way to pay this person ; flat rate, per viewing, etc. 

@Frederic BabeuxBoth of my parents are flat-landers (Manitoba) from farm families.  

The realtor I have selected charges a $6000 flat fee for any properties under $100,000. 

Hard to get excited about $480 per month minus operating expenses (assuming I understood correctly)...unless of course you know you can expand as many of your expenses will stay flat while you revenue will clearly go up. 

Most "traditional" Chicago 2-4 flats are constructed with the units vertically.  

I would talk to your lender more about it but most just flat out won’t allow it and can call the loan due if you transfer after sale.

If you can bake in the higher interests into your projections and still have strong numbers, it might be worth it. - Are there any state or regional gov't incentives to encourage investments?

From a psychological standpoint, I think it's easier to take a little increase every year compared to staying flat for a long time and then a big jump to try to catch back up to market, even if you end up paying less overall with the second option.