Is the total number too insignificant to see any real results and should I ramp up my list number or frequency?

Only time and life situations create motivation, not your direct mail piece.I hit different groups with different frequencies because they don't all respond at the same rate - varies by type of homeowner:-- Absentees - Monthly-- Owner Occupants - Every other month-- Probate - Every 2-3 monthsYou cannot create more motivation by mailing more often.  

I’m sure there are several individual cleaners in your area that would love the flexibility and frequency of a quick and ongoing $40 gig. 

Each time that period is going to be about 2 weeks in a good scenario, but I could be wrong.Steps 1-5 will take likely 2 weeks alone if you are interviewing multiple agents.I don't know what the frequency is of deals falling out from offer being accepted until final inspection, (best I can find is a article stating nationally 3.9% of sales failed in 2016, up from 2.1% in 2015)  but it's a considerable pain for any seller to have to reboot that process trying to appease a single fickle buyer. 

So, charging higher rent and increasing the frequency of turnovers can actually net you LESS money than charging less.

The frequency really depends on the class of property and tenant but every property should be inspected at least once a year.