Y'all just gave me much needed confidence to narrow my "niche." 

The neighborhood is very trendy and I really wanted to go for an edgy, industrial design but I was pretty nervous about whether I was making a mistake and would just end up narrowing my rental pool by being too style-specific.

Once you narrow down your areas you'll then want to make connections with experienced people that are familiar with the local market and it doesn't hurt to do your own research on the area as well.Cheap properties will normally carry a little higher risk. 

I would suggest you continuing to do your homework and once you think you have narrowed it down then ask for feedback or references. 

With only $3,300 as gross annual income, not considering management fees (if applicable), unplanned vacancies and other misc. expenses, that leaves a pretty narrow margin from an investor's point of view.

Narrow your search by county, and notice type.

You should have criteria, even if only to narrow down your search and allow you to truly understand the area where you'll be investing. 

This got me thinking I should buy another list, which I already have narrowed down, which is 1500 names, and buy more post cards.

If you just run the cash flow without considering value add, you are not getting the complete picture of the ROI IMHO and that narrow minded thinking will likely lead you out of the West and into the deepest ghetto in the Midwest, the South, etc., where it may be possible to make money but more often than not chews up and spits out newbies who focus solely on cash flow.

Hopefully the market is out-of-band right now and the test ad will give you an indication of demand during the "slow season."