Also, some households will use the laundry facilities more and some will use it less, so to cover your costs in an equitable manner, you could base the additional amount of rent on the number of people in the household.

I made the qualification  4x rent because the utilities for the house usually run $280/mo to $400/mo and I thought that if a household only makes $2250/mo (3x rent) in gross income, then their rent plus utilities could easily be more than 50% of their net income. 

This number will include your mortgage (if you didn’t do Baby Step 7 above), utilities, groceries, auto, household expenses, planned giving, and a little extra for fun experiences.

use your household income.....spouse maybe??

Establish your standards for total household income requirements (regardless of source) and stick to it.

I'd aim for using the same type of HVAC system for both units and separately metered if possible so each household pays for their own heat.For now, I suggest you invest in a few oil-filled portable electric heaters to have on hand in the event of a no-heat call.

This info will give you a decent idea of what to expect and help filter down your search to a few cities.Some of the metrics that the survey provides and that I find valuable to understand are:- Population - Home Values- Household Incomes- Rental Vacancy Rate- Homeowner Vacancy Rate- Poverty Rate- Educational Attainment Rate (High School/GED & Bachelors)- Number of Housing Unit- Rent to Income Ratio- Rent to Price Ratio- Population on SNAPS (supplemental nutrition assistance program) percentage- Property Tax Rate- Median Age of Buildings- Number of Structures by Units (SFR, Duplex, Triplex, Quadplex, etc...)- Median Rents by Number of Bedrooms- Unemployment Rate- Employment Sectors Percentages These are just some of the indicators that will help you understand the quality of an area as well as the kinds of returns one is to except.Also take into consideration the direction in which each of these market indicators are trending.

On 5+ units it goes down considerably per unit.I charge a RUBS - ratio utility billing system of $65 for household of 2 and +10 for each additional household member when it comes to water/sewer/trash and this usually comes out to 60-80% of actual costs (some markets you can get 100% back, but its not legal to get more than 100%).

There is a $25 limit for gifts per household. 

If you're both in the same unit, then it would be fair for both of you to share the household expenses.