Paul, I think it is not the quantity but the quality of your prospect tenants.

Sometimes paying a tiny bit more in points or interest is worth it--because that lender is ethical and clear. 

If you buy at a good enough deal, there will be buyers.Also, for the response rates and quantity mailed, there are two things that you should ask yourself that will help you determine your mailing quantity:1) Your budget (as @Justin Howe said)2) Your ability to handle the callsIt might help you to answer these questions if you had an idea on what to expect in respect to the response rates.

Your buyers list should be quality not quantity.

Quantity counts, do not get discouraged if a mail campaign goes unanswered.

Many wholesalers I've interacted with all have the same problem: Quantity over quality.

Quality, Quantity, and Frequency.

The downside is that this can be hard to manage so it is probably best to find a management company before you buy.7) Buy some land and build tiny homes, geodomes, yurts, or tree houses.

Tiny Homes  Also, have you watched the television show on Tiny Homes?

For example, search the forums here for a tiny glimpse on how many newer PMs/landlords complain about driving out to meet a prospect... only to be no showed or stood up by someone who had no intention or capacity to follow through from the beginning.Prescreening prospects to separate the window shoppers from those who meet and match your pre-determined, in-writing rental standards is critical to ensure you're not wasting anyone's time: theirs or yours.