I've had decent success using every door direct through the usps and finding a reasonable printer for postcards. I've found that 6"x9" work well. The key here is repeated exposure. I'd advertise to 10,000 ten times instead of sending out to 100,000 different houses. Better exposure and better targeting in higher end neighborhoods. It will also do you well to be as clean cut as possible and put your face right in the ad.
Also, there is no shame in going door to door looking for work. Be direct and brief. It helps a lot to have insurance, not only to cover yourself but also as a selling point, a lot of clients like that— some won't hire you without it. If you're going to run your own business, you're going to need to know sales fundamentals just as much as,maybe even more, so than working on the job.
Also I would like to upgrade to a four GPM unit as soon as you could, it really does make a difference in how fast your work goes but don't take on too much financially at first. And especially don't get into debt that you don't need. There's a ton of resources on the Internet. We are rooting for you!