It's generally advisable to have a lower ratio for better loan approval chances.Down Payment: Save for a down payment.

The GP share of the profit at the END of the deal also know as the PROMOTE is generally 20% to 30% of the profit (big picture high level). 

If the latter, could you buy a duplex and live in one unit and rent the other while still keeping your housing costs the same or lower than they are now?

I would recommend hiring a good property manager to minimize your stress level.  

At the lower price point, that's where people will compete against each other to drive up rents. 

I have tried lowering the price and advertising and only a couple bites with nothing substantial.

Your insurance premium (which you can get a quote for free in a few minutes or search the avg. insurance rates in an area), may be higher or lower depending on your location.

This shows why percentage makes no sense as the smaller property will have the lower maintenance/cap ex because it is smaller and likely will have tenant that takes better care of the unit  In your case you will have 2 kitchens, 2 furnaces, 2 water heaters, twice as many bathrooms, etc.

Our Initial plan was to renovate the lower unit, while we have the tenant upstairs and then renovate the top and live and occupy for a year-or two and then rent the top out and buy our next property.

Sometimes certain things fit a little better depending on what you are doing.Also, I might suggest that if you need something on a local level it's usually better to get this from another local real estate investor.